A cargo truck laden with more than two tons of explosives was detonated in front of Oklahoma City's nine-story federal building on April 19, 1995 — an act of terrorism that at the time was the worst such attack ever committed on U.S. soil.

The blast killed 168 people, including 19 children, injured hundreds more and caused hundreds of millions of dollars in damage to structures and vehicles in the downtown area.

President Bill Clinton led a memorial service for the victims as the FBI launched a nationwide investigation to find those responsible.

Within days, Timothy McVeigh and Terry Nichols were arrested and accused of conspiring to destroy the federal building in retribution for the government's handling of the siege of the Branch Davidian religious group at their compound in Waco, Texas, two years earlier.

McVeigh and Nichols were tried and convicted on federal charges, and Nichols was convicted of murder following a separate trial in Oklahoma. McVeigh was sentenced to death and executed and Nichols received multiple life prison sentences.

A memorial to the bombing's victims now sits on the former site of the federal building, and a nearby building that was damaged in the bombing houses an interactive museum.

Each year on the bombing's anniversary, family members of victims, survivors, rescue workers and others return to the memorial for a remembrance ceremony.