Friedrich Heinz Leibacher was born on 21 July 1944 in Zug, Switzerland, into a middle‑class family with two brothers. His behavioral problems emerged early. At the age of 13, he was arrested after publicly firing a rifle and threatening to kill his mother. His parents subsequently requested that he be placed in a reformatory. During his adolescence, he underwent multiple psychiatric evaluations. In 1960, at age 16, a psychiatrist formally assessed him as a potentially dangerous psychopath. He was released from the reformatory later that same year.

Following his release, Leibacher led an unstable and transient lifestyle. He worked intermittently as a clerical assistant and later attempted higher education. In 1965, he was deemed unfit for service in the Swiss Militia System. That same year, he obtained a secondary school diploma and briefly studied law at the University of Zurich. His studies ended abruptly after he was arrested for smuggling watches in Turkey, resulting in a seven‑month prison sentence.

Despite acquiring a business degree later in life, Leibacher remained largely unemployed or sporadically employed, including brief training as a waiter. He was repeatedly described in psychiatric and legal records as manipulative, exhibitionistic, and prone to aggressive behavior. Throughout the 1960s and 1970s, he accumulated a substantial criminal history, including assault, fraud, illegal weapons importation, public sexual offenses, and child molestation.

In 1970, he was convicted of child molestation and sexual offenses in public. Through fraudulent representation of his age, he received a youth sentence rather than an adult conviction, resulting in an 18‑month detention that was later converted to a work placement. Psychiatric evaluations from this period diagnosed him with schizoid personality disorder, hypochondriac tendencies, and a pronounced need for attention.

Leibacher later established a company, Media Zeitschriften AG, which authorities determined was used for illegitimate financial activities. Over the following decades, he was repeatedly accused of criminal acts, including illegal firearm importation, assault, arson for financial gain, and violent threats toward public officials and civilians. Despite multiple investigations and convictions, his sentences were often suspended or limited to warnings.

He married three times, all to women from the Dominican Republic, including two who were underage at the time of marriage. These marriages were brief and characterized by severe domestic abuse. He had three children. In 1994, he was arrested in the Dominican Republic for assaulting his third wife but avoided prosecution through bribery and returned to Switzerland with one of his children.

By the mid‑1990s, Leibacher was diagnosed with antisocial personality disorder, probable alcoholism, and symptoms of schizophrenia. He was granted an invalidity pension in 1995. Despite his extensive criminal and psychiatric history, his criminal record was expunged, and he was legally permitted to purchase firearms. In 1997, he acquired the assault rifle later used in the massacre.

On the morning of 27 September 2001, Friedrich Leibacher entered the Cantonal Parliament building in Zug, Switzerland, carrying four firearms and a homemade explosive device. The weapons legally purchased over the course of several years included a SIG SG 550 assault rifle, a Remington 870 pump-action shotgun, a Smith & Wesson revolver, and a SIG Sauer P232 pistol. He wore a self-made police vest and posed as a law enforcement officer to gain entry into the government building.

At approximately 10:32 a.m., Leibacher entered the assembly chamber during a regular session of the cantonal government. The parliament was in session with around 80 members present. According to witnesses, he announced, "Attention! This is a police operation," before opening fire on the gathered legislators. Over the next 2 minutes and 34 seconds, he fired 91 rounds, killing 14 individuals and wounding 18 others, including politicians, journalists, and staff.

Among the dead were three members of the Executive Council and eleven members of the Cantonal Council, marking the first instance of elected officials being killed in Switzerland since the 19th century. His apparent primary target, Director of Transport Robert Bisig, was unharmed, having survived by playing dead on the floor while Leibacher repeatedly called for him to show himself.

After initially exiting the chamber, Leibacher returned and threw a homemade bomb into the room. The device exploded, causing additional structural damage by blowing out windows and knocking doors off their hinges. No further fatalities occurred from the explosion. Shortly afterward, he returned to the hallway and, at approximately 10:34 a.m., fatally shot himself.

In his vehicle parked nearby, authorities discovered a suicide letter, titled “Tag des Zornes für die Zuger Mafia” (translated: “Day of Reckoning for the Zug Mafia”), in which he accused the cantonal government of systematic corruption and persecution. He left behind multiple copies of the letter as well as instructions for his cremation. Around his neck, he wore a written statement refusing medical aid and organ donation. Toxicology tests later confirmed a blood alcohol concentration of approximately 0.5‰, indicating he had consumed alcohol prior to the attack.

All of the firearms and ammunition used in the massacre had been legally obtained, despite Leibacher’s long history of criminal behavior and psychiatric evaluations identifying antisocial personality disorder and paranoid tendencies. His previous convictions including child molestation, public sexual offenses, illegal firearm imports, and repeated threats had been expunged, allowing him to pass background checks and purchase firearms lawfully.

The attack, though lasting under three minutes, had a devastating impact. The building was immediately evacuated, and national emergency protocols were activated. Police did not fire any shots in the response. Within hours, Swiss President Moritz Leuenberger declared a period of national mourning, and flags were flown at half-mast across the country.