When Alexandria jurors decided last June that two Mara Salvatrucha gang members should get life in prison for killing a 17-year-old government witness, they also made an unusual request about how the two men should spend that time: persuading other Latino youths to stay away from the most dominant gang in the Washington suburbs.

In formally sentencing Ismael Cisneros, 26, and Oscar A. Grande, 22, to life in prison yesterday, U.S. District Judge Gerald Bruce Lee joined the jury's attempt to stem the deadly violence that the gang, also known as MS-13, has spawned in recent years.

MS-13 "continues to prey on our youth and our community," Lee said moments before he issued the mandatory punishments. "I sentence you to life. What you do with it is up to you," he said. "The jury gave you ideas, and the court joins them."

Before their trial, Cisneros had told authorities that, if spared the death penalty, he would discourage adolescents from joining MS-13. He and Grande automatically were sentenced to life in prison without parole after the jury deadlocked on a death sentence, in part because the majority believed the men could serve as deterrents to at-risk youths.

In his remarks from the bench yesterday, Lee also addressed the Latino community as a whole, saying it was also the community's responsibility to reach out to youngsters who might be lured into joining the gang. Otherwise, "they will end up in courtrooms like this," Lee said.

Lee's comments came at the end of the 30-minute hearing, the final chapter in the two-month, high-profile trial in the slaying of Brenda Paz and her unborn fetus. Testimony shed light on the inner workings of the gang, which has been responsible for a number of killings, shootings and assaults in the suburbs, and exposed it, Lee said, as a "loosely organized group of homeless people" whose livelihoods are supported by begging for money and sleeping in crowded motel rooms.

Paz was killed, according to testimony, because she had cooperated with authorities investigating gangs in Virginia and across the country. The killing occurred just weeks after she had left the federal Witness Protection Program. Lee said the program did not protect her and called her slaying "unforgivable." Her body, stabbed numerous times, was found by a fisherman on the banks of the Shenandoah River. She was 16 weeks pregnant.

Dave Turner, a spokesman for the U.S. Marshals Service, said yesterday that there is "heartfelt disappointment" that Paz was killed and there "remains a determination to keep improving the program," under the oversight of the marshals. Paz brought with her to the program a "number of challenges," he said, and eventually was unable to resist the lure of the gang.

Paz left witness protection after only a few weeks. According to testimony in the trial, a federal safe house in Silver Spring where she stayed became a hangout for MS-13 and the scene of drinking and drug use. At hotels while in the protection program, she invited gang members to stay with her, and raucous parties occurred nightly.

"I want to apologize to the family of Brenda Paz and for all their suffering," Cisneros said yesterday in court, his shoulders shaking. In contrast, Grande said very little, asking that his visiting and phone privileges be restored.

Assistant U.S. Attorney Ronald Walutes, who said in court that Paz's family did not attend the trial because of a fear of MS-13, declined afterward to comment.

An attorney for Cisneros said that his client has renounced MS-13 and wants to spend his years in jail proposing solutions to the growing gang problem.

"As silly as it sounds, something good may come of this yet," said Jim Clark, one of two attorneys who represented Cisneros. "He really seems to have learned a lesson and is inspired to give something back."

The jury convicted Cisneros and Grande of five counts, including conspiracy to retaliate against a federal witness and killing a person aiding a federal investigation. It acquitted two other MS-13 members in Paz's death: Denis Rivera, 21, who was accused of ordering her slaying from jail, and Oscar Garcia-Orellana, 32. Rivera is serving a life sentence for another gang killing.

During the guilt phase of the trial, prosecutors called almost 50 witnesses, many of them former MS-13 members. They recalled the raucous parties, some at the FBI safe house in Silver Spring where Paz was staying, along with crimes ranging from vandalism to gang rapes.

Prosecutors said the gang issued a "green light" on Paz, code for an order to kill, after discovering that she was working with investigators in at least six states. A runaway from Los Angeles and Texas, Paz was known in the gang as "Smiley" for her wide smile and bubbly personality.

The final plan, prosecutors said, was hatched during a meeting at the Holiday Inn at Fair Oaks Mall the night before Paz's killing. Prosecutors said the defendants repeatedly stabbed Paz with two knives after luring her to the Shenandoah on the pretense of a fishing trip.

She "was pregnant and nearly decapitated and left to die in the woods," Lee said. "This murder was heinous, cruel and vicious."