For nearly five years, unsettling details have trickled out from dusty file cabinets and evidence vaults about just how much authorities and others knew before Eric Harris and Dylan Klebold slaughtered 12 classmates and a teacher at Columbine High School (search).
Misplaced police reports, prophetic videos made by the killers at the school itself, a father's secret journal, a Web site and essay promising death — families of the victims say the warning signs were clear.
"How many times have we heard this was everything, only for something else to come out?" asked Dawn Anna, mother of murdered student Lauren Townsend (search). "The first time we heard that was back in 1999."
Some 30,000 documents in the case have been released over the years and 10,418 pieces of evidence ranging from a tooth fragment to propane tanks were put on public display this year.
Local authorities, the school district, a state commission and the Colorado attorney general have all investigated, but the question remains: Why didn't someone — a parent, a sheriff's deputy, a teacher, a fellow student — step in before the suicidal gunmen went on their rampage?
Victims' families have tried to get answers: Some sued the sheriff's department, the school district and the parents of the killers. They won damages, but a federal judge sealed many records.
At the heart of most questions is the Jefferson County (search) Sheriff's Office, which responded to the massacre and led the official investigation. Its track record is spotty at best.
After the shootings, sheriff's officials downplayed tips about Harris making death threats — even though they relied on them to get a search warrant for his home hours after the bloodshed.
Randy and Judy Brown, whose sons were threatened by Harris, made several attempts to get the sheriff's department to investigate.
The tips started in 1997, when one of the Browns' two sons gave a deputy a printout of a Web site in which Harris boasted of going on nighttime missions with Klebold, firing weapons and vandalizing property.
The Web site later included boasts by Harris and Klebold about building pipe bombs and referred to "ground zero."
The tip was forwarded to former sheriff's investigator John Hicks (search). A warrant was drafted to search the Harris home, but it was never executed. A report by Hicks was found tucked inside a training manual just six months ago, a stunning revelation that prompted new Sheriff Ted Mink to ask Colorado Attorney General Ken Salazar to investigate.
Salazar said he found no negligence by the sheriff's department, though he found at least 15 instances of contact between law enforcement and one or both of the killers.
Other warning signs included violent videos made by Harris and Klebold for a class project and an essay by Klebold in another class describing a Columbine-like slaying of "preps." In one video project five months before the rampage, the two stalk through Columbine itself, offering hit man services to classmates tired of being bullied.
Harris and Klebold were arrested for a break-in a year before the attack, but parole officers were never told about the death threats tied to the teens. Both completed probation and were deemed to be likely candidates for success as adults.
"There was overwhelming evidence. Columbine should have been prevented," said Brian Rohrbough, whose son, Daniel, was one of the first to die. "We cannot turn back the hands of time, but we can put all this information out on the table. ... We can make this an example of what went wrong so that we can prevent it from happening again."
Most excruciating for some of those seeking answers is the fact that some information is being kept secret. The Harris and Klebold families were forced to give depositions to settle a lawsuit, but what they said remains sealed.
Joe Kechter, whose son, Matt, died at Columbine, said the lawsuit was settled because families were running out of money to fight the insurance companies whose homeowners' policies covered the Klebolds and Harrises.
"I hope some day the Klebolds and Harrises agree to get this information out so it can save other kids lives in the future," Kechter said. "I am doing this in respect of my son. I feel the police and the whole system let him down that day. I am not going to let him down."
The school district's investigation also remains confidential because officials say its release would violate attorney-client privilege. Salazar's investigation remains open, though family members don't expect big news from the new U.S. Senate candidate.
"I really don't think we are going to get any more answers," said Al Velasquez, whose son, Kyle, was among those killed.