In a report released Thursday, the grand jury also said it was "troubled" by still-missing documents in what remains the deadliest school attack in U.S. history. It was at least the third investigation to place no blame for the slaughter of 13 people by suicidal teens Eric Harris and Dylan Klebold.
Victims' families said the report confirmed their suspicions that the Jefferson County Sheriff's Office covered up mistakes that could have led authorities to the killers as much as two years before the attack.
"Clearly Columbine never should have happened and they don't want the public to know that," said Brian Rohrbough, one of several family members who met Thursday with Attorney General Ken Salazar. Rohrbough's son, Daniel, was among the students slain on April 20, 1999.
The grand jury said it didn't hand up any indictments because all the witnesses claimed to know nothing about the missing sheriff's records. The records involved a draft search warrant for Harris' house a year before the attack.
Salazar took the case to the grand jury after the sheriff asked him to investigate last fall.
The grand jury report said the draft affidavit, never submitted to a judge, was the subject of "a private meeting of high-ranking Jefferson County officials and law enforcement officials" called a few days after the attack to discuss the document and its "potential liabilities."
As a result of that meeting, the sheriff's office decided against discussing the affidavit at an April 30, 1999, news conference. A state district judge ordered the affidavit's release in 2001.
Jefferson County District Attorney Dave Thomas, who was at the post-attack meeting, said Thursday that was the first time he saw the affidavit and that it didn't provide enough evidence to warrant a search of the Harris home. His spokeswoman, Pam Russell, also said prosecutors weren't asked during the meeting whether investigators should publicly disclose the document.
Sheriff's spokeswoman Jacki Tallman declined comment on the report.
Randy and Judy Brown, who contacted the sheriff's office in 1997 and 1998 with complaints about Harris — including allegations he had threatened their son, Brooks — said the private meeting is evidence of a cover-up by authorities.
"This is collusion. This is criminal. This is a criminal conspiracy," Brown said after he and his wife met with the attorney general's staff.
At this point, investigations may have run dry in the massacre.
"The whole thing stinks to high heaven," said Scott Robinson, a criminal defense attorney, summing up the worst fears of survivors and families of victims: "There's nowhere to go from here."
Ken Lane, Salazar's spokesman, added: "There's nothing left to do."
Sheriff Ted Mink asked the attorney general to investigate last fall after coming across a 1997 report tucked inside a sheriff's department binder that dealt with a Web site where Harris referred to "ground zero" and boasted that he and Klebold had built pipe bombs. The report was apparently never pursued.
The attorney general's investigation revealed that the files of sheriff's investigator Michael Guerra, who wrote the proposed request for a search warrant, were missing. Salazar said earlier this year he had found no sign of negligence by the sheriff's department but said investigators were still looking for some documents.
After discovering the Guerra file was missing, Salazar asked the grand jury to investigate.
The grand jury said all the witnesses it heard from denied knowing what happened to Guerra's file. And it said that while the majority of documents in Guerra's file have been reconstructed, the originals are still missing.
Some computer files in the case have also been purged — some of them the summer after the attack — and other documents shredded, though that was done under normal department procedures.
The report could have reverberations in November — Thomas is running for Congress and Salazar is running for the U.S. Senate. Both are Democrats.
Thomas, who ran unsuccessfully for his party's nomination for Congress two years ago, said Columbine didn't cost him that race and would not hurt him this year. Thomas' opponent, Rep. Bob Beauprez, and Salazar's rival, Peter Coors, both declined to comment.