Hostouň:

• .380 ACP Škorpion semi-automatic pistol

University classrooms:

• 9mm Glock 47 semi-automatic pistol
• Sig Sauer semi-automatic pistol

University rooftop:

• .308 ZEV AR-10 semi-automatic rifle
• 12-gauge Francolin Guardian pump-action shotgun (suicide)

Deaths18 (including the perpetrator; 1 indirectly)Injured25PerpetratorDavid KozákMotiveRevenge on society

On 21 December 2023, 14 people were killed and 22 injured in a mass shooting at the main Faculty of Arts building of Charles University in central Prague, Czech Republic. Another three people were injured when the perpetrator opened fire toward the streets from the faculty's fourth-floor rooftop terrace. After having been engaged by the police, the perpetrator, 24-year-old postgraduate student David Kozák, committed suicide by shooting himself. Before the attack, his father was found murdered at his home in Hostouň.

At the time of the shooting, the perpetrator was one in a pool of about 4,000 suspects in a double murder case that took place six days earlier, 25 kilometres (16 mi) away, when a father and his infant daughter were murdered in Klánovice. The lead investigator confirmed that the police had not yet reviewed the perpetrator's potential as a suspect in the earlier killings when the Prague shootings took place. Still, evidence found in the latter event did link the two incidents.

The attack was the deadliest mass murder in the Czech Republic since its independence in 1993, surpassing the 2020 Bohumín arson attack.

On 15 December 2023, a 32-year-old father and his two-month-old daughter in a stroller were shot dead in Klánovice Forest on the eastern outskirts of Prague, approximately 25 kilometres (16 mi) away from the later Prague shootings. The police conducted a detailed search of the entire forest with hundreds of officers, while a special task force was set up in order to find the perpetrator. The police had no direct leads. The scope of investigation was first directed at owners of registered firearms matching the ballistic report from the crime scene, which initially limited the search to about 30,000 people. This was then further limited to 4.000, of which about 40 people lived in direct vicinity of the Klánovice forest. The initial investigation focused on those 40 people brought no leads. On 20 December, police said that they had no leads in the case but were continuing to search for the perpetrator.

After excluding a personal or work related motive, the police search turned towards possibility of a random murder. The firearms website zbrojnice.com noted a similarity of the case with the 2005 "Forest Killer" murders, in which a former police officer killed three random victims in forests in preparation for a planned mass murder in the Prague Metro, which was prevented by his early arrest; the article ended with an appeal to readers to remain vigilant and carry their concealed firearms.

Later investigation revealed that the perpetrator had previously visited the Klánovice forest only once. On the day of the University attack, Kozák had written a suicide note detailing the Klánovice murder on his computer, and had hidden the murder weapon in the family garden. According to the letter, he used public transport on the day of the murders, and switched off his phone while changing transport on the other side of the City of Prague. After arriving in Klánovice from Masaryk railway station, he continued into the forest. Kozák wrote that he was wearing ordinary clothing, thin-rimmed glasses, and a brown-beige backpack, and carried two handguns- a Beretta 71, and a Glock 45.

After walking along one of the trails, Kozák reached the main path and noticed a woman with two children at a nearby playground, and decided to target them. After loading his Glock pistol and attaching a silencer, he noticed a man with a stroller heading towards the playground, and decided that he was an easier target. The man stopped in front of the playground and turned left onto a path off of the main trail; Kozák followed him closely. Upon reaching a junction, Kozák raised his gun and fired multiple times at the man. The man apparently turned around and tried to cover his face with his hands; the attacker continued to shoot at him, firing a total of eight rounds at the man. He then fired two more rounds into the stroller before fleeing the scene.

Kozák fled towards Úvaly. Walking along a railway embankment, he noticed a couple with a stroller heading down a parallel path and considered shooting them as well, but decided not to after hearing sirens in the distance. Kozák boarded a bus that took him back to Klánovice train station. There, he boarded a train and left the area sometime between 16:00 and 16:45 in the afternoon.

The chief detective of Prague's 1st General Crime Unit stated because Kozák lived in the Central Bohemian Region, they were a few days short of being able to prevent the shootings. Central Bohemia is a separate region from the city of Prague, and each region in the country has a separate police directorate.

On 21 December 2023 at 12:19 CET, the Central Bohemian Police received a call from Kozák's mother. At 12:20 CET, Kozák's female friend K.C. called medical emergency line, stating that Kozák was planning to take his own life, that "he could be dangerous", that he told her "he will do something she will hear about", and that he was on route from his hometown of Hostouň to Prague. At 12:33, the police entered Kozák's home, and found the body of his father, who was killed by three shots into the head. The father was shot from behind while sitting at a table. His body was then moved on the floor, with his neck laid on a block of wood and with axe laying next to it with apparent intent to cut the head off, which the perpetrator didn't realize. A thorough search of the house at this time was hindered by improvised explosive devices, which were decommissioned by specialists later that day. The police found out that Kozák was a student of the Faculty of Arts at Charles University in Prague. A search warrant was issued and published; the warrant indicated that Kozák was armed and dangerous.

At 13:10 CET the Central Bohemian Police, where the Kozák's home was located, directly alerted the City of Prague Police. Prague police dispatcher issued an APB, according to which Kozák was sought due to suicide threats, he may be dangerous and also may be connected to a violent crime, possibly a murder. A security operation was commenced at Václav Havel Airport Prague, where Kozák worked, and where his father worked in the airport security department.

At 13:20 CET, Prague Police checked the Central Registy of Firearms, noting that Kozák owns multiple firearms, and that one of them was of the type which was the focus of Klánovice murders investigation. The APB was expanded with information that Kozák should be considered extremely dangerous.

At 13:23 CET the perpetrator entered the main building of the Faculty of Arts on Jan Palach Square with a heavy suitcase through the busy main entrance without arousing any suspicion. He proceeded to the fourth floor bathrooms, where he apparently remained until start of the attack. In the suitcase, he brought weapons, a large amount of ammunition, cleavers, chains and bicycle locks. Before starting the attack, the perpetrator placed under the bathroom window his ID, fourth floor plan with handwritten notes about classrooms capacities, unopened alcohol bottle and Rivotril pack of medicine.

At 13:30 CET two police units, altogether six officers, entered the main building of the Faculty of Arts on Jan Palach Square. where they talked to the reception personnel as well as to two Vice-Deans whom they met in the corridors. One of the officers searched premises of the School Library and adjacent bathrooms. They further searched through the ground floor and first floor, where they visited the Student Affairs Office and Department of History and learned about Kozák's lecture schedule, according to which he was supposed to attend a lecture starting at 14:00 in a different building on Celetná street.

At 13:57 CET, the dispatch sent multiple police units to evacuate the building of the Faculty of Arts on Celetná street, including the six police officers from the main building, who left without taking any further action there, and who would later stand guard at the Celetná building until the start of the attack in the main building. The evacuation of Celetná building was finished at 14:22. Kozák was not found in the building or in its vicinity. Multiple students walked from evacuated Celetná building into the main building.

At 14:04 CET, the dispatch relayed the following information through the police radio transmitter: "Increased caution for all patrols in the case of this Kozák. He's a really dangerous, very dangerous offender, suspect, and there's a lot of concern that he could use a weapon anytime, anywhere."

At 14:38 CET, Kozák's phone was turned on and registered by a telecommunications tower located near the Old Jewish Cemetery about 100 meters from the main building. The manhunt thus continued on the street level in this area, including Jewish Quarter, Pařížská street [cs], the Old Town Square and Staroměstská metro station. Dozens of heavily armed police officers, including Prague SWAT unit, spread out in this very crowded area, where Christmas markets were taking place.

Some plain-clothed criminal detectives moved from the Celetná building into the wider area of Jan Palach square in front of the main building. They did not enter the main building, as they had information that it had already been searched by other police units.

At 14:57 CET, as the manhunt continued, the police received their first calls about a shooting taking place in the main Faculty of Arts building on Jan Palach Square, a twelve-minute walk from the evacuated building on Celetná. The perpetrator had opened fire from a pistol inside the building's fourth floor corridors and classrooms at 14:54. The perpetrator repeatedly entered classroom No. 423, targeting everyone who was present inside. Once he moved further away from this classroom, one of the students led remaining survivors in their effort to barricade the entry door. All of the people in this classroom were either killed or suffered life-threatening injuries.

Several of the students present in other 4th floor classrooms fled through windows towards the terrace, then climbed an exterior ledge on the other side of the building and later jumped to a third-floor balcony, sustaining injuries from the fall. While trying to escape on the ledge, student and athlete Klára Holcová [cs] fell off the building to her death.

At 15:02 CET first officer, a criminal police detective, entered the building. He was then joined by uniformed policemen at 15:05 CET with dozens of policemen coming in afterwards. After the arrival of the police, no gunshots were heard from within the building. Based on information given by students, the police searched for the perpetrator on the upper floors, while other officers started evacuating students from the lower floors to the Rudolfinum across the street.

At 15:11 the police officers who were searching for the perpetrator on the upper floors were alerted that he was shooting from a rifle towards the streets, with mistaken information that the perpetrator was on the rooftop, while in reality he was on 4th floor top terrace. The gunfire also caused panic outside, with crowds fleeing Charles Bridge. Police lost some time searching for a route outside, as the area was difficult to navigate. While the first three floors are accessible by the main central staircase, the position of the side staircase leading to the fourth floor was not immediately visible to the officers.

At 15:12, the advancing police forces split into two groups, with the first continuing their search for the perpetrator and the second initiating first aid to the victims. Authorities reported seeing "piles of ammunition" inside the building's corridors, adding that Kozák had brought multiple weapons into the university. The city emergency services also deployed a large number of ambulance units to the scene.

A video by reporter Jiří Forman showed Kozák on the 4th floor terrace with a rifle. Forman, who had taken cover, shouted at Kozák to shoot in his direction in a successful attempt to draw his fire away from students evacuating the building.The perpetrator was visible several times only for a few brief moments, as he was moving mostly out of view on the terrace. The perpetrator fired the last of his 13 shots from the AR 10 rifle at 15:18:51.

Between 15:18:54 and 15:18:59, as the perpetrator was again briefly visible, a plaincloth detective that was positioned at the Jan Palach square fired three shots from his Glock pistol. The distance was about 105 meters. Subsequently at 15:19:10, the perpetrator threw his loaded rifle off the roof, and then at 15:19:24 committed suicide by a self-inflicted head shot wound from shotgun.

Two police officers armed with G36 carbines climbed to a top floor of a hotel on the opposite side of the street. At 15:18:57 an officer aimed his carbine at the perpetrator through the closed window, but didn't take the shot before the perpetrator's surrender; available information leads to conclusion that the perpetrator was not aware of the police presense in the opposite building.

Police officers reached the perpetrator's body on the terrace at 15:25. Meanwhile, at 15:23, the other groups of policemen entered classrooms 423 and 417, where majority of the victims were situated, and started providing first aid.

A 32-year-old man and his two-month-old daughter were killed in Klánovice Forest on 15 December 2023. Kozák's father was killed at their home in the early morning of 21 December 2023.

Twelve people were killed within the University building, one died from injuries at a hospital and one died when she fell after slipping from the ledge when trying to escape the perpetrator. Twenty-two people were injured (ten critically) within the University, some of them from injuries sustained while jumping from a fourth floor ledge to a third floor balcony. Three people were injured when the perpetrator opened fire towards the streets.

Two of the victims were staff members, including Lenka Hlávková, head of the Institute of Musicology of Charles University, and Jan Dlask [cs], a lecturer at the university's Department of Germanic Studies. Among the remaining fatalities were students.

Ten of the injured were in serious condition, one of them being a daughter of MP and member of the parliamentary committee for education Jan Richter (ANO) [cs], who criticized police for allegedly wrongly triaging his daughter as a low-priority victim who subsequently nearly bled to death before reaching a hospital. Three foreign nationals were reported to be among the injured: one Dutch and two Emiratis.

The perpetrator also hit a civilian vehicle and police cars.

On 9 January 2024, the police's Department of Internal Investigation presented the conclusion of its inquiry into police conduct in the case. The Department's director Michal Tikovský stated that they had found no mistakes in the police's handling of the case. He added that "The officers' actions were in accordance with the applicable legislation and internal regulations. The police intervention can be assessed as prompt and professional." Tikovský said that the police could not have known that the perpetrator was heading towards the main building, nor that he was preparing to carry out a mass murder. Applicable rules had also been followed when issuing the perpetrator's gun license.

The Parliamentary Security Committee requested the Department's closing report. On 6 February 2024, they received a fifty-page report, in which 33 pages were completely redacted and the remaining 17 pages were mostly redacted. On page 39, it was stated that "it cannot be concluded that the police knew that the lives of the students of the Faculty of Philosophy in the building on Jana Palach Square were in real and immediate danger." Opposition ANO party members were angered by the redaction of the document and stated their intent to establish a Parliamentary Inquiry Commission with full investigative powers in order to receive complete information about the case.

"They were covering it up from the beginning, that no one could have expected what he would do, and that it would be just a normal suicide. I think the arsenal of weapons he had, the fact that he killed his father and planted a bomb in the house, should have led everyone to know that this was not normal."
Father of one of the victims

While the police intervention after the attack had started was generally accepted as correct, a strong criticism was aimed at apparent mistakes in its search for Kozák before the University attack. In January 2024, the Chief of Prague Police Petr Matějček was defending the police procedure with explanation: "We were still working with the idea that the man was a danger to himself and was going to commit suicide." Interior Minister Vít Rakušan also commented that authorities had no indication of anyone else at risk other than Kozák himself, and that police knew that the father was murdered only after decommissioning the improvised explosive device, which took place after the University attack was over.

However, that was in contradiction with the information provided by the K.C. in the initial phone call and the murder scene within the house. According to Lidové noviny, the circumstances of the father's death were clearly pointing to murder, police also had information about Kozák's firearms possession, and Matějček personally ordered a tactical unit to be present in the Staroměstské náměstí area before the attack commenced. Moreover, on 26 June 2024, online daily Seznam zprávy published action reports filed by the policemen that had unsuccessfully searched for the perpetrator in the School of Arts main building. Three policemen signed under first report wrote that they were searching for Kozák "suspected of murdering his father". Report of the other unit explicitly stated: "He was suspected of murdering his father while threatening suicide. Other information suggests that he is a mentally disturbed man who also possesses several weapons."

During 24 June 2024, Parliamentary Security Committee hearing, Matějček further alleged that it was technically impossible for the police officers who entered the building at 13:30 to review the security camera footage at that time. The footage later revealed the perpetrator's entry at 13:23. University official labeled Matějček's statement as a "lie", claiming that reviewing of previous footage can be done immediately, but the police officers asked for it only hours after the attack. The university's information about availability of the camera footage was later confirmed also by the spokesman of the Regional Directorate of the Police of the Capital City of Prague Jan Daněk, who claimed it would in any case not be helpful, as Kozák was not facing the camera, had black hair and a different hairstyle compared to photo available to the police officers. Also, during the Committee's hearing, Matějček repeated the statement that there was no initial information that the perpetrator might commit a murder or a mass murder, but later added that he had been considered a murder suspect in relation to his father's death. Matějček admitted that the police were aware that one of his firearms was of the type which was the focus of Klánovice murders investigation. He also stated that the police sent "everything they had" into the centre of Prague.

Police issued a formal decision on conclusion of investigation in June 2024. Multiple victims, their relatives as well as the Charles University filed appeal against the decision. The relatives were especially outraged by the fact that police officers entered shortly after the perpetrator, but didn't properly search the building, didn't order evacuation of the students, nor did any police officers remain within the faculty's main building. Prague Police Chief Matějček stated that the police officers "followed a hot lead", and therefore remaining in the main building would be "counterproductive". Matejček further said that if evacuation of the building had taken place, the perpetrator would have become aware of it and "anything could have happened".

Several relatives of murdered students as well as some journalists called for resignation of the Minister of the Interior Vít Rakušan, the Police President [cs] Martin Vondrášek [cs], and in particular the Prague Police Chief Petr Matějček, who was accused by the media of falsely implying that Central Bohemian Police didn't provide correct information, and thus Prague Police was not aware of Kozák's dangerousness. On 27 June 2024, Echo24 [cs] daily accused Rakušan and Matějček of "covering evidence" and "undermining people's trust in the state". Rakušan reacted by stating that he only had information from public sources and that he "hopes that the police will explain any inconsistencies."

General Inspection of Security Forces, which is tasked with investigating crimes of police officers, concluded its investigation at the beginning of June 2024. On 6 June 2024, its director Vít Hendrych informed members of the Parliamentary Security Committee that no crime was committed by any police officer in the case. Opposition ANO members of the committee unsuccessfully requested the inspection's closing report. Hendrych stated that full fifty-page report is confidential and that even police will receive only a three-page summary. The three-page summary was released on 9 July 2024, with media noting that it doesn't answer any of the pertinent questions, such as what exact information police had while searching for Kozák, and especially why did the police officers leave the main building before the attack commenced.

Leading opposition party ANO repeatedly requested establishment of Parliamentary Inquiry Commission which would investigate conduct of the police in the case. The governing parties repeatedly refused such a step, with head of Parliamentary Security Committee Pavel Žáček stating that they have "full trust in the police and the state attorney office". This, however, changed following the June 2024 formal conclusion of investigation and after the hearing of the Parliamentary Security Committee. First, the Czech Pirate Party broke ranks with the rest of the Government and announced it would support the opposition's vote for Inquiry Commission. On 26 June 2024, the ANO's proposal for establishment of the Commission was approved in the Chamber by vote of 132 of 141 deputies. The Commission has the power to procure documents, demand explanations and interview witnesses and, depending on the nature of the case, hire an expert and an interpreter.

The evening after the attack, passersby lit candles and left flowers at the site of the attack. The Charles University Foundation and the community of Klánovice announced humanitarian online fundraisers to help those affected by the tragedy. The 2023–24 UEFA Women's Champions League football match between Slavia Prague and St. Pölten, set to be played at home in Prague on the day of the shooting, was postponed. Several other sports and cultural events were also called off, while Christmas markets across of the country were either closed or reduced operations on 23 December. Interior minister Vít Rakušan called on mayors across the country to cancel New Year's fireworks displays in light of the killings and urged citizens to mark the event peacefully out of respect for those traumatised by the shootings.

Following the shooting, police detained four people on suspicion of threatening to stage copycat attacks or expressing approval of the incident, while police presence in selected sites, including schools, were heightened until 1 January 2024.

Authorities responded to several false alarms about potential attacks following the incident, including two bomb-related hoaxes in Prague and in Václav Havel airport. In Slovakia, a 64-year-old man in Žilina was arrested by police after calling emergency services and saying that he intended to do "what happened in Prague" on the evening after the attack. He was subsequently charged with spreading general alarm.

At some point after the shootings, Kozák's house in Hostouň was broken into, and subsequently put under police guard.

On 4 January 2024, a march was held from the main building of Charles University to the Faculty of Arts building to commemorate the victims of the shootings, after which students formed a human chain around the building in a symbolic embrace before lighting a fire at Jan Palach square as bells in nearby churches tolled for 14 minutes.

On 26 January 2024, the Chamber of Deputies of the Czech Republic passed a new firearms act which had been in the making since 2017 and which was formally publicly introduced in September 2022. The new act, which will become effective in 2026, includes several changes, such as requiring businesses to report suspicious purchases of firearms and ammunition to police, requiring gun owners to undergo a medical examination every five years as opposed to 10 years under the current laws, giving doctors access to databases to find out if their patients are gun owners, and expanding reasons for preliminary seizure of firearms by police. The legislation passed unopposed in the lower house, and must be approved by the Senate and President Petr Pavel for it to become law.

On 14 June 2024, the Czech police closed the investigation. The report was first provided to the relatives of the victims, and later to the general public. Investigators concluded that the shooter was a lone assailant, that the attack was not planned to target anyone in particular, and that the motive was that he felt misunderstood by society and wanted to draw attention to himself.

On 20 June 2024, a memorial for the victims of the attack was installed in Jan Palach Square. It weighs approximately eight tons and is a three meters high piece of sandstone. It was designed by Vojtěch Adamec and placed down by architect Vojtěch Králíček.

The perpetrator was identified as David Kozák (b. 12 August 1999), a 24-year-old masters in world history student from Hostouň, 21 kilometers (13 mi) outside Prague, who had graduated with a bachelor's degree in History and European Studies from the Faculty of Arts. Kozák successfully defended his bachelor's thesis at the Institute of World History, Faculty of Arts, Charles University, entitled The Antagonism problematics of Galician Peasant Revolt and Kraków Uprising in the year of 1846. The supervisor was professor František Stellner [cs]; the thesis was defended with an excellent grade. Kozák's thesis was subsequently awarded the Marian Szyjkowski Award by the Polish Institute in Prague [cs].

The perpetrator had no prior criminal record, and had also passed an enhanced background check by the Civil Aviation Authority as part of a hiring process for his job at the Václav Havel International Airport.

According to State Attorney Jana Murínová, Kozák had been watching videos with "bizarre violence and bizarre pornography". In particular, he was watching pornography originating from Asia, including movies in which actresses were made to look like zombies or corpses.

His father was generally considered to be a very gentle, kind and helpful person, while his mother had been the authoritative figure in the family. According to the psychologist, the family didn't provide functional emotional and supportive relationship to the perpetrator. Conflicts with parents played role in the development of perpetrator's suicide tendencies. Classmates testified that Kozák described being under stress due to parent's pressure to finish the bachelor's degree early. Kozák also described being punished for failing to do home chores. He further described having little sleep, eating little and drinking only a green tea. Perpetrator's mother contradicted these testimonies, claiming that the perpetrator was a calm and happy boy and that the family functioned well, adding that she doesn't understand his actions.

Kozák was unable to establish partner relationships, with unsuccessful attempts to find a girlfriend during high school. His feeling of loneliness deepened when he started studying at the university, and in particular during the COVID-19 restrictions. One of the witnesses of the University killing spree testified Kozák saying while murdering his victims: "You don't talk to me much. You don't communicate with me much."

Interior Minister Vít Rakušan said the authorities did not suspect an ideological or extremist link. On 26 April 2024, state attorney Jana Murínová stated during a public hearing of the Parliamentary Security Committee that the perpetrator was not suffering from a mental disorder.

A Telegram account attributed to him contained writings in fluent Russian that praised two school shooters from Russia, namely Ilnaz Galyaviev and Alina Afanaskina, and described suicidal tendencies. This information was shared by Czech media but was not officially confirmed by police. A Russia correspondent at Czech Radio suggested the Telegram account was likely fake, as one post was edited after the shooter's death and the posts were written "in the language of a young native Russian speaker". Police made no definitive conclusion regarding the Telegram account, citing refusal of Russian authorities to cooperate in the case.

"At least in the last year of his life, David Kozák was characterised by a long-lasting and strong incitement to murderous activity. The correlation of the homicidal urge were the feelings of injustice, resentment and hatred. By the end of 2022, he showed an association between suicidal and homicidal ideation."
Psychologist expert opinion (post mortem)

Czech Police Chief Martin Vondrášek [cs] said that the perpetrator had a gun license and owned eight firearms, which he obtained as part of his plan to commit a mass murder. As a European Union member state, the Czech Republic adheres to the European Firearms Directive and legal accessibility of firearms is comparable to other EU countries. In 2021, a constitutional amendment to the country's Charter of Fundamental Rights and Freedoms codified the citizens' right to defend themselves or others with a weapon. To legally possess a firearm in the Czech Republic, a person must first obtain a firearms license, which requires, among other things, a medical examination. A bill of health is issued by the general practitioner, who can also request a review of the applicant's mental state.

Kozák's friend, who has been named only as K.C. by the media, became worried about his mental state in summer 2022. Due to her intervention, Kozák underwent four visits with a psychiatrist between September and November 2022. Here, Kozák disclosed first suicidal thoughts, but during the visits progressed towards also murderous ideas aimed at his parents as well as unassuming other people. The psychiatrist advised that Kozák starts visiting a psychologist, which he did only once in December 2022.

Psychiatrists in the Czech Republic have legal duty to send their medical reports to the patient's general practitioner, "if the practitioner is known to them". As Kozák didn't disclose name of his general practitioner, no report was sent. Lidové noviny however cited several psychiatrists, according to whom it is easy to find information about patient's general practitioner. They claimed that it "takes only three clicks" through online communication channel with the patient's insurance provider. The Czech Medical Association [cs] confirmed that a psychiatrist may learn about the general practitioner in this way, however there is no legal requirement to do so. Due to absence of his general practitioner, Kozák's medical clearance was issued by a substitute doctor, who specializes in chinese medicine and who graduated Guangdong Medical University. The police asked the Czech Medical Association to review whether a substitute doctor may issue a medical clearance instead of the general practitioner, as required by the law.

The general practitioner could have learned about Kozák's psychiatric visits from an online database of the patient's medical prescriptions. However, reviewing this information is not obligatory and the general practitioner that issued the bill of health failed to do so. The only information in the bill of health for the gun license was that Kozák must wear glasses when using firearms.

According to police ordered post-mortem psychological evaluation, Kozák had personality that was "schizoid with narcissistic and dissociative traits and a very solid IQ", but did not suffer from any particular mental disorder.

In September 2024, vice-chairman of Parliamentary Defense Committee Pavel Růžička, together with Minister of Defense Jana Černochová and other deputies, lodged a proposal to ammend the Firearms Act to remedy the errors in the process of health clearance which were uncovered during the investigation.

Police concluded that Kozák had been planning to conduct a mass murder for a long time. He researched information about mass murderers, including the Forest Killer, The Spartakiad Killer and a Norwegian killer.

From beginning of 2023, Kozák gradually changed his lifestyle in a way aimed at imitation of Keiji Kiriya from All You Need Is Kill Japanese science fiction, which had previously been the topic of an essay he wrote at high school. In September 2023 he limited his planning to the University and its vicinity. He researched teaching schedules of the fourth floor classrooms and downloaded floorplans both of the building where he attacked as well as the other school building at the Celetná street. He made notes of probable number of students in each of the classrooms. He was further researching public events at the nearby Rudolfinum building, Jan Palach square and other locations at the Prague Old Town.

Kozák received a gift of CZK 300,000 (approximately USD 13,000) from his grandmother and liquidated CZK 400,000 (USD 17,000) from a long-term savings account. This money as well as income from his airport job was used towards purchases of firearms and ammunition.

Kozák had told several friends about his gun purchases. He shared most information with his friend K.C., whom he informed also about undergoing shooting courses. On 3 November 2023, the perpetrator told K.C. that he started exercising as he will have to carry heavy bags in a month or two. On 6 December 2023, Kozák wrote messages to K.C., which, in hindsight, according to the investigators show clear determination to commit a murder.

During a vigil at Charles University on 22 December, its rector Milena Králíčková said, "The academic community is shaken, deeply shaken." Prime Minister Petr Fiala cancelled his scheduled events in Olomouc and travelled to Prague shortly after the shooting. President Petr Pavel expressed his "sincere condolences" to the family and friends of the victims via social media, while also cutting short a trip to France.

Fiala later announced a day of mourning for 23 December, with flags flying at half-mast and a minute of silence held at noon, along with the ringing of bells for the victims. A mass for the victims was also held that day at Saint Vitus Cathedral, which was attended by Pavel, Senate president Miloš Vystrčil, and Chamber of Deputies president Markéta Pekarová Adamová. The service was officiated by Jan Graubner, the Roman Catholic Archbishop of Prague, who expressed shock at the incident and expressed the "need to clearly condemn what happened" while also looking into the future. University rector Milena Králíčková also said during the event that "Nobody should be left alone in these tough moments." Religious services for the victims were also held in other parts of the country.

In a social media post, SPD MP Jiří Kobza blamed the "inclusive progressive school system" at the Faculty of Arts for creating the shooter. The post was later deleted. The Czech Rectors Conference [cs] called Kobza's post "absolutely shocking, crossing the boundaries of decency, morality, good manners, but also the boundaries of humanity." Charles University announced it would file a criminal complaint against Kobza. On 9 January 2024, Kobza apologized on social media, claiming he was under emotions at the time of his initial post. Charles University called his apology "unsatisfactory" and too late.

Many international leaders expressed condolences, including European Commission president Ursula von der Leyen, United States president Joe Biden, Ukrainian president Volodymyr Zelenskyy, Canadian prime minister Justin Trudeau, Israeli president Isaac Herzog, Slovak president Zuzana Čaputová and prime minister Robert Fico, German chancellor Olaf Scholz, Hungarian prime minister Viktor Orbán, French president Emmanuel Macron, Finnish president Sauli Niinistö, Pope Francis, and Taiwanese president Tsai Ing-wen.

• Uherský Brod shooting, a 2015 mass shooting that was the deadliest mass shooting in the Czech Republic prior to this attack
• Ostrava hospital attack, a 2019 Czech mass shooting

• Police bodycam compilation, released by the Police of the Czech Republic
• Police decision on conclusion of investigation, published by Echo24 [cs]