After the incident, speculation began immediately about Hinrichs' motivation and the number of accomplices, if any. An off-duty police officer had noted Hinrichs talking with a local feed store owner about ammonium nitrate and had begun an investigation. There was innuendo regarding the Pakistani heritage of the bomber's roommate. Terrorism-related speculation was heightened after the explosive agent was found to be TATP, an explosive of similar manufacture, though separate makeup, to the compound used in the July 2005 London bombings, the attempted destruction of an airplane by a shoe bomber, and by Hamas in clandestine devices for use by suicide bombers. The Federal Bureau of Investigation (FBI) and local authorities concluded in 2006 that Hinrichs acted alone and had no assistance from other groups. They could not prove or disprove allegations that Hinrichs intended to enter the packed stadium and kill football fans along with himself.