The murders of Abigail Williams and Liberty German, also known as the Delphi murders, occurred on February 13, 2017, in Delphi, Indiana, United States. Their bodies were discovered near the Monon High Bridge Trail, part of the Delphi Historic Trails, from where the girls disappeared the previous day. The murders received extensive media coverage, in part due to video and audio recordings released by law enforcement that came from German's smartphone, which recorded an individual believed to be the killer.

The case remained unresolved for six years until 2022 when Richard Allen was arrested and charged with the murders. He was found guilty in 2024 and sentenced to 130 years in prison.

At 1:35 p.m. on February 13, 2017, 13-year-old Abigail Joyce Williams (born June 23, 2003) and 14-year-old Liberty Rose Lynn German (born December 27, 2002) were dropped off by German's older sister, Kelsi German, on County Road 300 North, east of the Hoosier Heartland Highway. The girls were hiking on the Monon High Bridge over Deer Creek, among woodland in remote Deer Creek Township. At 2:07 p.m., German posted a photo of Williams walking the bridge; after this, they were not heard from again. They were reported missing at 5:30 p.m. after they had failed to meet German's father at 3:15 p.m. The families initially searched for the girls themselves before calling the police. Authorities who quickly searched the area did not initially suspect foul play in the disappearance. This would change when the bodies of the girls were found around noon the next day, about 0.5 miles (0.80 km) east of the abandoned Monon High Bridge. The bodies were found on the north bank of Deer Creek.

Police did not initially release details of how the girls were murdered. As early as February 15, 2017, Indiana State Police began circulating a still image of an individual reportedly seen on the Monon High Bridge Trail near where the two friends were slain; the grainy photograph appears to capture a Caucasian male, hands in pockets, head down, walking on the rail bridge, towards the girls. A few days later, the person in the photograph, dubbed the "Bridge Guy", was named the prime suspect in the double-homicide.

On February 22, law enforcement released an audio recording during which the voice of the suspect, although muffled, is heard to say, "Down the hill." At this news conference, officials credited the source of the audio and imagery to German's smartphone and further regarded her as a hero for having had the presence of mind and fortitude to secretly record the exchange. Police indicated that additional evidence from the phone had been secured, but would not release further details so as not to "compromise any future trial." By this time, the reward offered in the case was set at $41,000.

On July 17, police distributed a composite sketch of someone sought as a person of prime interest in the murders. The sketch was apparently created from eyewitness accounts of a hiker on the Delphi Historic Trails the day the girls vanished.

On April 22, 2019, Indiana State Police announced a "new direction" in the case and released a new sketch of the suspect, while urging the public to look at the sketch, listen to the audio, watch how the man walks on the bridge and send tips to the tipline email. Investigators stated they had reason to believe that the suspect might be hiding in plain sight and was almost certainly familiar with the Delphi area, from living there, working there or for other reasons. An additional plea was made for help in identifying the driver of a vehicle left abandoned off the Hoosier Heartland Highway in Delphi, at the former Child Services office, between noon and 5 p.m. on the day of the murders.

In September 2022, investigators reviewed a misfiled tip after a volunteer file clerk discovered the error. Richard Allen's last name was recorded incorrectly on the tip when submitted, and the file was therefore wrongly marked as "cleared"; the file clerk deduced that the tip from years earlier was regarding Richard Allen, and brought it to the case's investigator. In the tip, Richard Allen self-reported three days after the murders to being on the trails on the day of the murders and reported seeing Williams and German.

On October 26, 2022, Richard Allen was taken into custody and appeared in court on October 28. On October 31, 2022, Indiana State Police announced that Allen had been charged with two counts of murder in the case. He had pled not guilty. Time described the arrest as "the first major break in a case that has captivated national attention for nearly six years." His trial, originally scheduled to start March 20, 2023, was postponed to allow the defense team to review discovery materials. Two public defenders were appointed to represent Allen.

On November 29, 2022, Judge Frances Gull issued an order to unseal the probable cause affidavit that led to Allen's arrest. According to the redacted document, video footage recovered from German's phone showed one of the victims mentioning "gun" as a man wearing a dark jacket and jeans approached them and ordered them to go "down the hill". Investigators believe Allen is the man seen in the video. Investigators also found a ".40-caliber unspent round" less than two feet from one victim's body, but between the two victims. It was later determined that the round came from a gun owned by Allen. A witness said she saw a man walking away from the bridge "wearing a blue colored jacket and blue jeans and was muddy and bloody." Another witness and a tip mentioned that a car was parked "oddly" and appeared to be parked in a way as if to hide its license plate. Investigators said the description of the vehicle matched a vehicle that Allen owned in 2017.

According to a probable cause affidavit, Allen was interviewed by the police in 2017, and said he was on the trail that afternoon for around two hours. The document also said that in a subsequent interview in October 2022, Allen told authorities he had worn "jeans and a black or blue jacket" that day and had gone to the bridge to "watch fish".

Richard Matthew Allen (born September 1972) grew up in Mexico, Indiana. Allen was a student at North Miami Middle/High School in neighboring Denver where he participated in football, track and field until graduating in 1991. Allen attended Ivy Tech Community College where he studied accounting, and had a short stint in both the U.S. Army and National Guard. Allen was later married and had two children. From 2003 until 2013, he worked as a store manager at a Logansport Walmart. He later worked at two CVS Pharmacy stores, one in neighboring Peru and the other in Delphi, before receiving his pharmacy technician license in February 2018. Public records show that Allen relocated to Delphi from Mexico in December 2006.

Shortly after his arrest, Allen told authorities that he was at his mother's house in Peru while his wife was working. Allen estimated that he left the house around 11:15 a.m., and arrived on the Monon High Trail around an hour later. Allen said that he saw three girls passing by on the trail, before stating that he did not see anybody else afterward. Allen said he then went on his phone to watch the stocks ticker while walking on the trail before deciding he could not find his black 2016 Ford Focus SE on the trail property. After finding his vehicle and driving back to his mother's Peru home, Allen said he continued to watch the stocks. Afterward, Allen said that he told his wife that he was on the trail the day the girls went missing. His wife mentioned that the police were looking to talk to people who may have information, so he said he went to the sheriff's office and spoke with a Department of Natural Resources officer days after the two girls were killed.

On December 2, 2022, Judge Gull issued a gag order until January 2023. Allen's defense attorneys argued in a motion to move the trial out of Carroll County, based on concerns about juror bias due to what the attorneys described as the "extensive media attention" and the "highly publicized nature of the case" in the local area.

In October 2023, Judge Gull removed the defense attorneys citing gross negligence due to crime scene photos being leaked from their office. The attorneys' removal was appealed to the Indiana Supreme Court in which the justices of the Indiana Supreme Court reinstated the defense attorneys to the case.

The trial began on October 18, 2024, in Delphi. During the trial, prosecutors stated both girls had their throats cut. Williams was found fully clothed, whereas German was discovered nude. An unspent .40 caliber bullet from Allen's gun was found between the bodies. Prosecutors said that Allen had admitted to the murders more than 60 times while incarcerated, confessing to "his wife, his mother, family members, the prison warden, the psychologist who treated him in prison, other prison employees and other inmates." The confessions were made in person, over the phone, and in writing. Prosecutors told the jury that Allen was the "Bridge Guy" after showing them a digitally enhanced 43-second version of the cellphone video recorded by German. A State Police Master Trooper, who had listened to more than 700 of Allen’s prison phone calls, testified that "the voice of the 'Bridge Guy' is the voice of Richard Allen".

A clinical psychologist who worked for the Indiana Department of Corrections Behavioral Health testified on behalf of the defense that Allen was "diagnosed with a serious mental illness" and that he had a "grave disability". She testified that Allen told her that he had "originally planned to sexually assault the victims but ran away when he saw a van nearby, and he had cut the girls' throats and covered their bodies with sticks." The defense hired a neuropsychologist from Carmel who testified at trial that Allen had "pretty severe depression" and work-related stress and anxiety.

The jury, which had been sequestered during the trial, began deliberations on November 7. On November 11, 2024, Allen was convicted on all counts. On December 20, 2024, Judge Gull sentenced Allen to 65 years for the murder of German and 65 years for the murder of Williams, with the terms to be served consecutively, resulting in a total of 130 years in prison. Allen was then transported to the Reception Diagnostic Center in Plainfield, where he's currently serving his 130-year sentence.

In response to a request from German's mother in 2017, homeowners across central Indiana installed orange lights on their front porches, to commemorate the girls as well as to indicate that the murderer remained at large at that time.

In August 2017, the families announced their plans to build a sports complex for Delphi in memory of the girls. A non-profit organization, L & A Park Foundation, was formed to "celebrate and commemorate the lives of Libby German and Abby Williams by creating a place for the appreciation of nature, art, play, and athleticism for generations to come." A site was procured a mile north of Delphi, and in the years following the girls' deaths, continued progress has been made in the development of Abby and Libby Memorial Park. In 2020, the L & A Park Foundation was named a recipient of the NBA All-Star 2021 Legacy Grant.

The Delphi Community Middle School, which both girls attended at the time of their murders, renamed the school's library to the "Abby and Libby Memorial Library".

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• Delphi Homicide Investigation – Indiana State Police
• Information Sought in Investigation into Deaths of Liberty German and Abigail Williams – FBI Indianapolis Field Office
• Seeking Information on Unknown Suspect in Indiana Double-Murder Investigation – Federal Bureau of Investigation