During his adolescence in upstate New York, Timothy McVeigh developed an enthusiasm for guns and a suspicion of governmental authority. He drew inspiration from the 1978 novel The Turner Diaries, written by the white nationalist William Luther Pierce, which depicts a right-wing insurrection against a tyrannical federal government seeking to deprive citizens of their right to bear arms. But this was only the beginning of McVeigh’s anti-government stance.

As a soldier in the U.S. Army, McVeigh won a medal for bravery in the Persian Gulf War, but after his discharge in 1991 he began frequenting gun shows and developed even stronger suspicions of the U.S. government.

Then came the notorious Ruby Ridge standoff of August 1992, when U.S. marshals attempted to apprehend a man named Randy Weaver at his family’s remote hillside cabin in northern Idaho. Weaver, who had resisted efforts by the Bureau of Alcohol, Tobacco and Firearms (ATF) to force him to inform on the white supremacist group Aryan Nations, hadn’t shown up for his trial on weapons charges.

An initial exchange of fire left Weaver’s 14-year-old son and a U.S. marshal dead. Federal authorities then laid siege to Weaver’s cabin for 11 days, during which an FBI sniper wounded Weaver and family friend Kevin Harris and killed Weaver’s wife, Vicki.

McVeigh viewed Ruby Ridge as clear evidence that the U.S. government aimed to disarm the public and take away people’s Second Amendment rights.

McVeigh reacted even more strongly to federal authorities’ handling of a 51-day standoff with members of the Branch Davidian religious sect near Waco, Texas. Like Ruby Ridge, the Waco siege began with an ATF raid; it ended in a fire that killed around 75 members of the millennial sect in April 1993.

McVeigh was far from alone in his outrage: Ruby Ridge and the events at Waco fueled anger within the fledgling American militia movement and other far-right groups at what they saw as an oppressive government determined to attack and suppress anyone who (like Weaver or the Davidians) refused to conform to its will.

On April 19, 1995—exactly two years after the fiery conclusion of the botched Waco siege—McVeigh detonated explosives planted in a truck outside the Alfred P. Murrah Federal Building in Oklahoma City. He plotted the attack with two fellow Army veterans who shared his anti-government views, Terry Nichols and Michael Fortier.

The building housed offices for the Social Security Administration, the Drug Enforcement Administration (DEA), the Secret Service and the ATF, among other organizations. It also housed a veterans’ counseling center, a military recruitment office and a daycare center.

The Oklahoma City Bombing killed 168 people, including 19 children, and wounded hundreds more, in the worst terrorist attack in U.S. history to that date.

Before he was executed in 2001, McVeigh made it clear that he intended the bombing as retribution for the deaths at Waco and Ruby Ridge, and had deliberately planned the bombing to take place on the second anniversary of the Waco disaster.