A U.S. citizen blew up a Federal Building in Oklahoma City.
From the link above: Carried out by Timothy McVeigh and Terry Nichols, the bombing killed 168 people and injured more than 680 others. The blast destroyed or damaged 324 buildings within a 16-block radius, destroyed or burned 86 cars, and shattered glass in 258 nearby buildings, causing at least an estimated $652 million worth of damage.
An estimated 646 people were inside the building when the bomb exploded. By the end of the day, 14 adults and 6 children were confirmed dead, and over 100 injured. The toll eventually reached 168 confirmed dead, not including an unmatched leg that could have belonged to an unidentified 169th victim. Most of the deaths resulted from the collapse of the building, rather than the bomb blast itself. Those killed included 163 who were in the Alfred P. Murrah Federal Building, one person in the Athenian Building, one woman in a parking lot across the street, a man and woman in the Oklahoma Water Resources building, and a rescue worker struck on the head by debris.
The victims, including three pregnant women, ranged in age from 3 months to 73 years. Of the dead, 99 worked for the federal government. Eight of the victims were federal law enforcement agents; four from the United States Secret Service, two from the United States Customs Service, one from the United States Drug Enforcement Administration, and one from the United States Department of Housing and Urban Development. Nineteen of the victims were children, 15 of whom were in the America's Kids Day Care Center. The bodies of the 168 victims were identified at a temporary morgue set up at the scene. A team of 24 identified the victims using full-body X-rays, dental examinations, fingerprinting, blood tests, and DNA testing. More than 680 people were injured. The majority of the injuries were abrasions, severe burns, and bone fractures.
McVeigh later justified his killing of children in the bombing: "I didn't define the rules of engagement in this conflict. The rules, if not written down, are defined by the aggressor. It was brutal, no holds barred. Women and kids were killed at and Ruby Ridge. You put back in [the government's] faces exactly what they're giving out.