Eric Harris and Dylan Klebold leer into the camera and promise to murder bullies. "If you ever touch him again, I will fricking kill you," Harris yells at an imaginary thug. The newly released videos were filmed by the two boys in the months before they killed 12 students and a teacher (and themselves) at Columbine High School in April 1999. The disturbing images were part of a one-day display of more than 10,000 items collected during the investigation, from murder weapons to body bags.

As the fifth anniversary of Columbine approaches, questions linger about whether the horror could have been prevented. "There is an institutional cover-up of the crimes at Columbine," says Randy Brown, whose son escaped the rampage. Brown is "obsessed" with investigating what police and school officials knew before the shootings. His office is filled with task-force reports, FBI documents and press clippings. "My wife and I," he says, "we do this every day." The Browns met with police in August 1997, a year and a half before the shootings, to complain about threats by Harris against their son. Then, on March 31, 1998, the Browns showed police threats that Harris made on his Web site. An officer began working on a search warrant of Harris's house, but was reassigned to other investigations, and the case "went to the bottom of the pile," according to a 39-page report from Colorado Attorney General Ken Salazar, who is looking into the actions of the Jefferson County Sheriff's Office. Salazar says police had at least 15 contacts with the killers in the years before the shootings, ranging from complaints about Harris's violent Web site to a van break-in. That fact disturbs Darrell Scott, whose daughter Rachel was killed. "None of us knows what to believe anymore," he says.

Salazar says there was no "nefarious plot" by police to ignore evidence that violence could erupt at Columbine. But asked whether officials in the Sheriff's Office tried to cover up mistakes, he replied: "I do not know." The A.G. has not given a timeline for completing his investigation. And Brown says he will continue his crusade--because the families who lost children "just don't have the strength to do this."