A Colorado judge today sentenced Mark Manes, 22, to six years in prison for illegally selling a handgun to Eric Harris and Dylan Klebold that the two teenagers used in last April's massacre at Columbine High School.

Manes was sentenced to concurrent six- and three-year terms for selling a handgun to a minor and possession of a sawed-off shotgun following an emotional afternoon of testimony by surviving family members of the deadly assault and the reading of a transcript of a dramatic videotape left behind by Klebold and Harris.

In the videotape, obviously made with full understanding of what they were about to undertake, the two thanked Manes and another friend who has yet to be sentenced for helping "us do what we needed to do." But on the tape they also said that neither Manes nor Phil Duran--also charged with helping provide the handgun--knew of their plans.

On the tape, Harris says: "Oh, I'd like to make a thank you to Mark and Phil. Very cool. You helped us do what we need to do. Thank you." But he also says, in what is apparently a message to police: "Don't arrest any of our friends, don't arrest any of our co-workers, don't arrest any of our family members, don't arrest anyone 'cuz they didn't have a [expletive] clue."

Citing the "grievous harm" that stemmed from Manes's sale of a TEC-DC 9 handgun to the killers of 12 Columbine students and one teacher, District Judge Henry Nieto said he had no choice but to sentence Manes to prison despite the recommendation of the Jefferson County probation department that he receive a probationary sentence.

"The conduct of this defendant was the first step in what became an earthquake," said Nieto. Despite the fact that Manes had cooperated with police, had pleaded guilty to the two charges in August, had insisted he had no idea what Klebold and Harris had in mind, and had become a model young adult after a troubled youth, Nieto said: "All of us have a moral duty when we see the potential for harm to intervene."

Manes, briefly addressing the judge and a courtroom packed with dozens of victims' family members, said he had "no idea anything was going to happen" when he sold the weapon--and, the night before the shootings, 100 rounds of ammunition--to the two teenagers. "There is no way I can adequately express my sorrow to the families of the victims of Columbine," said Manes, who was "horrified" when he heard of the April 20 shootings. "It is something I will regret for the rest of my life."

The TEC-DC 9 semiautomatic pistol Manes sold to Klebold last January was fired 55 times during the assault on Columbine, and was responsible for the deaths of four of the victims and the wounding of two. Twelve students and one faculty member were killed and 21 others wounded before Harris, 18, and Klebold, 17, committed suicide in the school's library.

In their testimony today, relatives of some of the victims told of the deep and lingering scars left by the shooting, and repeatedly asked Nieto to send a message to the nation by sentencing Manes to jail.

"Thirteen beautiful lives have been taken tragically and unfairly," said Kristen Townsend, whose sister Lauren, 18, was among the dead. "Did Mark Manes shoot and kill my sister? No. . . . But he sold the weapons and he must be punished for it," she said.

Manes bowed his head and looked at the defense table as Townsend and other victims' relatives testified. Many among the relatives wept, particularly when two videotapes were shown chronicling the lives of Townsend and Matt Kechter, 16, also killed in the assault.

Steve Jensen, deputy district attorney for Jefferson County, painted a harsh portrait of Manes in asking the judge for a lengthy jail term, describing him as a repeated troublemaker as a juvenile and a chronic drug abuser and dealer as a young adult.

In an emotional defense of his client, Robert Ransome strenuously challenged Jensen's portrayal of Manes, saying his scrapes with the law grew out of a difficult childhood with two older adopted siblings who were retarded and whose needs left his parents no time to nurture him. Manes, Ransome said, overcame that period, stopped abusing drugs, attended college and became a valued systems administrator at a Denver area computer company.

"His character today . . . is exemplary," said Ransome. "He is not the type of person we put in prison."