In addition to the shootings, the attack involved several homemade bombs. Two of these were placed in the cafeteria, powerful enough to kill or seriously injure all people within the area, although they failed to detonate. Their cars in the parking lots were made into bombs which also failed to detonate, and at another location away from the school, two bombs were set up as diversions, only one of which partially detonated. The motive remains unclear; but Harris and Klebold planned the massacre for around a year, and hoped the massacre would cause the most deaths in U.S. history, which then meant exceeding the death toll of the Oklahoma City bombing; "USA Today" referred to the Columbine massacre as "planned as a grand, if badly implemented, terrorist bombing."