They were the most notorious yet least-seen artifacts from one of the worst school shootings in American history — roughly four hours of home videos made by two teenage killers-to-be, shot in the last weeks of their lives and offering glimpses into the methods and motives behind the 1999 attack on Columbine High School that killed thirteen people and seriously injured two dozen more. The so-called "basement tapes" of Eric Harris and Dylan Klebold have been the subject of intense litigation and media speculation, morbid curiosity and outrage, half-baked psychoanalysis and earnest requests from violence-prevention researchers to make them available for study.

And now they're history — but not the way the gunmen thought they would be.

See also: Are Columbine's Remaining Secrets Too Dangerous for the Public to Know?

Law enforcement officials have always regarded the tapes as a particularly infectious form of toxic waste, a primer in mass murder that could inspire more violence and must never be released. That's no longer a problem: A spokesperson for the Jefferson County Sheriff's Office, the agency that took custody of the videos hours after the shootings, recently confirmed that every known copy of the basement tapes has been destroyed.

"I am not aware of any copies that are out there in anyone's hands," says Jacki Kelley, the JCSO public information director. "We actually held on to a lot of evidence from the Columbine investigation longer than our retention policies require."

Kelley says Sheriff Ted Mink approved the destruction of the tapes — along with shell casings, weapons and other remaining Columbine evidence — in early 2011. The obliteration of the videos was only acknowledged recently, though, after a private party filed an open records request seeking access to the basement tapes. A response from the county attorney's office noted that the sheriff's office "no longer has any documents in its possession responsive to your request."

Mink, who completed an eleven-year stint as sheriff in 2014 and is now a deputy director at the Colorado Bureau of Investigation, says he wanted to ensure that the rantings of Harris and Klebold — who go into some details in the tapes about bomb-making and other preparations, express hopes that others will launch similar attacks, and say they expect to attract followers "because we're so fucking godlike" — never surface on social media.

"That was my call," Mink says. "My decision. I can't tell you how to measure prevention. I feel in my own heart it was preventative."

But some social scientists have contended that the tapes, along with writings by the killers and other videos they made, could be helpful in understanding the psychology of school shooters and recognizing warning signs. "A number of people have seen them and written about them," notes Del Elliott, founding director of the Center for the Study and Prevention of Violence at the University of Colorado Boulder. "Their value by themselves I don't see as critical. But the fact that we're losing information that could have been available some time in the future is distressing."

Several victim families, as well as the killers' own parents, had favored suppressing or destroying the tapes, fearing they would inspire copycat killings. But some families had pressed for their release, seeing Jeffco officials' reluctance to disclose evidence as part of a larger pattern of cover-ups and misinformation that plagued the Columbine investigation. A few contended that releasing the tapes would de-mythologize the killers, showing them to be angry, deluded, self-obsessed and far-from-godlike adolescents.

"When you have Islamic terrorists cutting off people's heads on YouTube, it's hard to look back on those tapes and say they shouldn't be released," says Brian Rohrbough, whose fifteen-year-old son, Dan, was killed at Columbine.

The quiet destruction of the tapes, he adds, only deepens his distrust of the sheriff's office: "There was a copycat shooting immediately after Columbine, and you can make the argument that this stuff shouldn't be released for a while. But all those arguments go out the window when you consider the way [former Sheriff] John Stone and [former Jefferson County District Attorney] Dave Thomas deceived the families about what they knew."

The content of the tapes was one of the most closely guarded secrets of the Columbine investigation during its first few months — right up until the point that Jeffco officials provided exclusive access to the materials to a reporter from Time magazine, leading to a lurid cover story and community outrage. Stone then arranged a hasty viewing of the tapes by some local media outlets and victim family members, the only time the tapes — or at least some portion of them — have been publicly screened.

Continue for more about the destruction of the Columbine killers' basement tapes. In 2001, after first Westword and then the Rocky Mountain News published extensive excerpts from Eric Harris's journal, the Denver Post went to court to demand that the rest of the materials seized from the killers' homes be released, including the basement tapes. The case dragged on for five years. After the Colorado Supreme Court ruled that the materials were criminal justice records, under the control of the sheriff's office, Sheriff Mink decided to release the writings of Klebold and Harris but keep the video and audio recordings the pair made in the vaults. (Other videos, including several made for school assignments and one showing the pair test-firing their weapons, had already been released.)

There were discussions about allowing violence-prevention researchers some form of limited access to the tapes, but Colorado's open records laws don't contain provisions for such an arrangement. "We were all very much under the impression that it would be an all-or-nothing release," Kelley says.

The tapes also became highly restricted exhibits in civil lawsuits filed against a pharmaceutical company and the killers' parents. Following the settlement of those cases, U.S. District Judge Lewis Babcock ordered that the parents' depositions be turned over to the National Archives and Records Administration and kept under seal for twenty years. It's not clear to what extent some exhibits may also have been preserved, but a separate decision by Babcock ordered that the copies of the tapes used in the litigation be destroyed.

Is every known copy of the tapes now gone? Mink and Kelley think so. Other sources claim there's at least one bootleg audio recording of at least some of the tapes, and partial transcripts of the material have circulated online for years — including one summary released by the sheriff's office itself. But text isn't the same as video, and Mink feels he's done all he can to ensure the tapes don't end up on YouTube.

Mink is comfortable with his decision, reached after conferring with experts from the FBI's famed Behavioral Analysis Unit, who told him that the tapes would be a "strong motivator" to violence for other suicidal or homicidal youth.

"The consensus from the scientists in the room was that there was no value to these," Mink says. "They saw nothing there. They only saw the potential for further violence if these tapes got into the wrong hands."