The Zug massacre took place on 27 September 2001 in the city of Zug (Canton of Zug, Switzerland) in the canton's parliament. Friedrich Leibacher shot dead 14 people before killing himself. Leibacher was armed with a civilian version of a Stgw 90, a SIG Sauer pistol, a pump-action shotgun, and a revolver, and wore a homemade police vest.

In the years before the massacre, Leibacher drew attention to himself through repeated lawsuits. These were dismissed, so he assumed he was being persecuted by the state and felt he had to resort to violence. In the aftermath of the shooting, gun laws in Switzerland were tightened and changes in security were enacted.

On 27 September 2001 at 10:30 a.m., Leibacher entered the canton's parliament building and started shooting in the hall where the members of parliament were meeting. Leibacher was armed with a civilian version of a Stgw 90 (Swiss Army assault rifle), a SIG Sauer pistol, a pump-action shotgun, and a revolver, and wore a homemade orange police vest. Leibacher was able to enter the parliament building without problem.

He killed three members of the Executive Council ("Regierungsräte") and eleven members of the legislature ("Kantonsräte"), and wounded 18 politicians and journalists, some heavily. He fired 91 rounds. He then ignited a homemade bomb and took his own life. His main intended target was the Cantonal Minister Robert Bisig, who was unharmed. Leibacher left a suicide note titled "Tag des Zornes für die Zuger Mafia" ("Day of rage for the Zug mafia"), which referred to his belief there was a plot against him.

Leibacher had several failed marriages to women from the Dominican Republic, with one of whom he had a daughter. In 1970 he was convicted of child molestation, incest, theft, forgery and traffic offences, and sentenced to 18 months' detention. He served his sentence in a work-training institution.

After leaving detention, Leibacher became unemployed. Doctors diagnosed him with paranoid personality disorder and alcoholism and he received an invalidity pension.

In 1998 he was convicted of threatening a bus driver employed by the Zug transport company with a gun, after the driver claimed he had been drinking. Leibacher was upset by his treatment, and wrote frequently to the authorities and public figures with letters of complaint. The canton then sued Leibacher for defamation. The passage of time did not diminish his grievance as Leibacher began to believe he was the target of a government conspiracy led by Robert Bisig, a member of the cantonal government. He sued Bisig, but in the days before the shooting, his action and six of his other cases were dismissed by the court.

During the months prior to the shooting, Leibacher closed his bank accounts and sold his shares. The day before the shooting, he instructed a Swiss funeral home that when he died he was to be cremated and have his ashes scattered across the Atlantic. All of the guns Leibacher owned were legally acquired. He was able to buy a pump-action shotgun nine days before the shooting, despite the fact he was under surveillance at the time for threatening someone with a gun.

Afterwards, many local parliaments increased their security or installed security measures. Some established a strict access control for visitors and security passes for the politicians and staff. After the shooting, the cantonal authorities filed to claim Leibacher's estate, valued at SFr400,000. In the aftermath of the shooting, gun laws in Switzerland were tightened. The mayor of Zug described the scene as "a terrible scene of horror" and the shooting as an "attack on our democracy".

On the national level, the Sektion Sicherheit Parlamentsgebäude (section for the security of parliament buildings) was established as part of the Bundessicherheitsdienst (Federal Security Service), a police unit of 35, which secures the Bundeshaus in Bern. As part of a general electronic access control for visitors, access controls with X-ray machines were installed. Further, separate wings of the Bundeshaus were secured with gates, which have to be opened with an access badge/card.

In part due to the attack along with a high rate of gun suicide, as well as the murder of Corinne Rey-Bellet in 2006, a referendum was held in 2011, proposing the ban of the sale of fully automatic weapons and pump-action rifles, and that military-issued firearms must be held in army depots. The referendum was rejected by voters.

• Romanshorn shooting
• Nanterre massacre
• List of attacks on legislatures
• List of mass shootings in Switzerland

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