Members of a violent Northern Virginia street gang lured a 17-year-old pregnant federal witness to the Shenandoah River on the pretense of taking her fishing, but then stabbed her repeatedly and told her they were killing her because she had cooperated with law enforcement, authorities charged yesterday.

The plot, federal officials said, was masterminded from a Northern Virginia jail cell where one of the gang members was awaiting trial on murder charges.

Four members of Mara Salvatrucha, or MS-13, were indicted by a federal grand jury in Alexandria in the death of Brenda Paz, another gang member who left the federal witness protection program last June, about a month before her tattoo-covered body was found on the banks of the river.

Paz had cooperated with detectives in at least six states against MS-13 and was scheduled to be a witness in a federal murder case in Alexandria. One of the men later convicted in that slaying, Denis Rivera, 20, of Alexandria, was charged yesterday with orchestrating Paz's slaying from jail. The others charged -- Oscar Antonio Grande, 21, of Fairfax, Ismael Juarez Cisneros, 25, of Vienna and Oscar Alexander Garcia-Orellana, 31, of Fairfax -- wielded the knives that killed Paz, prosecutors said.

All four were charged with killing a federal witness, witness tampering and retaliating against a witness. They could face the death penalty or life in prison. Prosecutors said a decision has not been made on whether to seek death.

Citing taped telephone calls and intercepted mail, the indictment alleges that the four men investigated whether Paz was cooperating, determined that she was and lured her on the supposed fishing trip. Rivera, known within the gang as "Conejo," or "Rabbit," is quoted as saying at one point that he would plant Paz "in a park."

Told of Paz's stabbing, the indictment says, Rivera said the lesson for gang members or anyone else is that those who "rat on Conejo" die: "They rat and that's it."

Rivera's attorney in the Alexandria slaying case, Robert L. Jenkins Jr., said he had not seen the new indictment and could not comment. The three other defendants had not yet been appointed lawyers.

The indictment marks another escalation in the federal crackdown on MS-13, which is active throughout the region and is the largest and most violent street gang in Northern Virginia. Federal prosecutors are conducting a broad grand jury probe, which sources have said is aimed at crippling the gang by targeting its leaders.

Paul J. McNulty, the U.S. attorney in Alexandria, called the indictment "a major step forward in a united effort by law enforcement to attack gang violence in Northern Virginia. Those who threaten or retaliate against witnesses will be dealt with in the severest terms."

The region's growing gang problem has been attracting increasing attention from politicians and law enforcement, especially since last month's gang-related machete attack that nearly severed the hands of a Fairfax teenager and the slaying a few days later of a Herndon youth. Underscoring that concern, 13 state and federal law enforcement officials stood behind McNulty at a news conference announcing yesterday's indictment.

Paz, who was known as "Smiley" within MS-13, grew up in Los Angeles as the daughter of a gang member. In September 2002, the indictment says, she began cooperating with the federal probe of the gang, revealing to FBI agents and prosecutors "her extensive knowledge of MS-13."

She said, for example, that Rivera had told her of his involvement in the September 2001 slaying of Joaquim Diaz, 19, who was lured into the woods on federal land in Alexandria, stabbed repeatedly and nearly beheaded, according to the indictment. Paz said Rivera had told her that cutting Diaz's throat was "like cutting through a chicken," the indictment says. Rivera and another MS-13 member were convicted in Diaz's killing and sentenced to life.

Paz was put in an FBI safe house and then into witness protection. But people who knew her have said she left because she missed the allure of gang life. Soon after she returned to Northern Virginia in June 2003, MS-13 began plotting her slaying, the indictment says.

The three other defendants -- who are jailed on unrelated charges but were free at the time of the slaying -- communicated with Rivera, who was jailed in Arlington and Fairfax counties. At one point, the indictment says, Rivera had another MS-13 member call Paz at a hotel in Kansas City, Mo., while Rivera secretly listened in from his cell.

After Paz told that gang member that Rivera would be lucky if the federal government didn't "kill him," the indictment says, MS-13 concluded that Paz was talking.

Asked whether Paz's slaying could have been prevented, McNulty said that federal authorities did everything they could to protect her but that her departure from witness protection had "exposed her to enormous risk."

Greg Hunter, an Arlington lawyer who was Paz's court-appointed guardian, yesterday recalled a phone conversation he had with Paz days before her death in which he pleaded with her to reenter witness protection. Despite his urging, he said, she insisted that she would stay on the street.

"She was convinced the marshals wouldn't take her back, and she was convinced she could handle this," Hunter said.

John F. Clark, the U.S. marshal for the Eastern District of Virginia, said it had been too difficult for officials monitoring Rivera's calls from jail to piece the plot together before Paz's death. "With the slang they used and code and this sort of street kind of gang dialect, it was not readily discernible," he said.

Brenda Paz Convicted murderer Denis Rivera is charged in the death of a witness.