2005 University of Oklahoma bombing

On the evening of October 1, 2005, at approximately 7:30 p.m. CDT, a bomb detonated near George Lynn Cross Hall on Van Vleet Oval at the University of Oklahoma's main campus in Norman. The site was less than 200 yards from Oklahoma Memorial Stadium, where 84,501 spectators were attending a football game between the Oklahoma Sooners and Kansas State Wildcats. The person responsible for detonating the device, 21-year-old OU mechanical engineering student Joel "Joe" Henry Hinrichs III, died in the explosion. No other person was killed or injured.

Spectators inside the stadium heard the explosion, with some describing it as sounding like distant thunder; reports indicated it was audible up to five miles away. University officials delayed making an announcement until near the end of the game, directing attendees to exit through specific gates and avoid the South Oval area, in order to prevent panic. Initial reports mistakenly described a second device and identified hydrogen peroxide as the explosive; investigators later determined the explosive was triacetone triperoxide (TATP), which Hinrichs carried in a bag estimated at two to three pounds.

An off-duty Norman police officer had overheard Hinrichs discussing the purchase of ammonium nitrate with a feed store owner two days before the bombing and had begun an investigation, which was still underway when the explosion occurred. A computer check found no outstanding warrants or criminal record for Hinrichs. Searches of Hinrichs' apartment the following morning uncovered additional TATP, precursor chemicals, a suicide note displayed on his laptop, and records of prior explosive experiments conducted at Red Rock Canyon in Caddo County.

In the aftermath, speculation about terrorism and possible accomplices circulated, partly fueled by unfounded rumors concerning the Pakistani heritage of Hinrichs' roommate and Hinrichs' possible religious affiliation. As many as eight people, including OU student Hakim Mansouri, OU physics researcher Djamal Rabli, and OU Arabic instructor Hossam Barakat, were detained for questioning by Norman police in the early hours of October 2, 2005, and again the following day, before being cleared of suspicion. The president of OU's Muslim Student Association stated he did not believe Hinrichs was Muslim.

In July 2006, the FBI formally concluded there was no evidence Hinrichs was a terrorist and no indication he acted with assistance from any other individual or group after interviewing more than 200 witnesses. Investigators could not prove or disprove rumors that Hinrichs had intended to enter the stadium; there was no evidence he attempted to buy a ticket or enter the venue, and security footage did not show him near stadium entrances. Officials suggested Hinrichs may have become careless while handling the unstable TATP shortly before the device detonated.

In November 2006, Hinrichs' brother, Thomas Carlisle Hinrichs, was arrested after allegedly attacking their father and threatening to kill an FBI agent; he was convicted in June 2007 and sentenced to 37 months in prison in October 2007. In August 2007, the university conducted an emergency preparedness drill simulating a gas line rupture inside the stadium, described as the first such university stadium drill in the United States.