Earlier, law-enforcement sources said the videotape from the cafeteria showed Harris and Klebold firing their guns at the propane tank bomb, hoping to set it off. But neither Davis nor lead investigator John Kiekbusch would comment on that this week. Nearly two months after the massacre at Columbine, officials say they are continuing to interview witnesses but don't offer any other information. Klebold and Harris killed 12 students and a teacher before turning their weapons on themselves. While authorities haven't completely ruled out the possibility that they had assistance from a third gunman, Davis has said they are leaning toward the belief that the two acted alone.
Investigators also continue to explore whether anyone else had prior knowledge of the attack.
So far, just one arrest has been made in connection with the massacre. The cafeteria surveillance tape was enhanced at the FBI's Quantico, Va., lab and was returned about three weeks ago, Davis said. Investigators studied hours of the April 20 tape, from early morning that day until mid-afternoon. That's when the siege was finally over and fire sprinklers were still running in the cafeteria. After everybody left, the sprinklers were running .