Authorities released a chilling video Wednesday showing the Columbine gunmen chuckling as they fire a handgun, rifles and a sawed-off shotgun at trees and bowling pins.
At one point they talk about the damage that could be done by bullets.
"Imagine that in someone's (expletive) brain," one of the teens says.
The video, taken on a shaky handheld camera on a snow-covered hillside in national forest south of Denver, is the first made by the gunmen themselves to be released to the public.
It came from one of the men who went to prison for helping the two teens get the guns, reports CBS News Correspondent Lee Frank.
Among other scenes, the video shows a smiling Harris blowing across the upturned muzzle of a shotgun like a gunslinger. Both teens wear trench coats, and later show the camera hands made bloody by a gun butt.
"Guns are bad. When you saw them off and make them illegal, bad things happen to you," one says. The two then point at a gun and mockingly spank it as Klebold says, "no, no, no."
The two repeatedly point to shattered bowling pins and giggle about entry and exit holes. The boys were in a bowling class hours before the shootings began.
The video shows at least four different weapons, including automatic rifles, shotguns and a pistol.
The Jefferson County sheriff's office long ago released surveillance video showing the suicidal teenagers as they entered the Columbine High School cafeteria during the attack on April 20, 1999.
The latest video was released as part of an ongoing effort by the sheriff's office and a task force established by the attorney general to examine evidence assembled during the Columbine investigation. The goal is to release as much evidence as possible to the public.
Randy Brown, a member of the task force, picked up a copy of the videotape. He and his wife warned sheriff's deputies more than a year before the shootings that Harris had threatened to kill one of their sons, and have been strong critics of authorities' handling of the response to and investigation of the massacre.
"The videotape is important," Brown said. "What's really important is did the sheriff see it, did the school see it, or did the parents see it? How many opportunities were missed to stop these two killers?"
The video also shows Mark Manes shooting some of the weapons. Manes sold Harris and Klebold a TEC-DC9 semiautomatic handgun for $500 about three months before the massacre. The gun was used in the attack.
Manes pleaded guilty to providing a handgun to minors and possessing an illegally sawed-off shotgun and was sentenced in 1999 to six years in prison. He was released to a halfway house after less than two years.
Also along on the shooting excursion was Jessica Miklich, Manes' girlfriend. The video shows her shooting one of the rifles, a trench coat hanging on a tree in the background.
The man who taped the target practice was Philip Duran, who worked with Harris and Klebold at a pizza shop, Jefferson County district attorney's spokeswoman Pam Russell said.
Duran, who was accused of introducing Harris and Klebold to Manes, was charged with providing a gun — the TEC-DC9 — to a minor and possessing a dangerous or illegal weapon, a sawed-off shotgun. He was sentenced in June 2000 to 4½ years in prison.
In a videotaped message before the attack, the gunmen thanked Manes for providing the gun, saying they couldn't have done it without his help. They also warned him that he and Duran would probably be blamed for helping with the assault.
Lawsuits to release the so-called "basement video tapes" — made by Harris and Klebold in the months before the attack — are pending. The sheriff's office has allowed reporters to watch the tapes, but has not released copies to the public.