A member of the Mara Salvatrucha street gang yesterday became the second person convicted in a regionwide effort to target the violent gang using broad federal racketeering laws.

Alirio Reyes, 26, pleaded guilty in U.S. District Court in Alexandria to federal charges in the slaying of a Herndon teenager, prosecutors said. Reyes admitted that he shot Jose Sandoval, 17, in May 2004 because Sandoval said he was a member of a rival gang.

The slaying of Sandoval heightened awareness of the Washington area's growing problem with such gangs as Mara Salvatrucha, or MS-13. It came less than a week after a gang-related machete attack on a 16-year-old youth in the Alexandria section of Fairfax County. Collectively, the episodes triggered a flurry of interest from politicians and led to more law enforcement task forces and increased anti-gang education efforts in the region.

Reyes and a fellow MS-13 member, Osmin Heriberto Alfaro-Fuentes, were indicted in December on racketeering and other counts. The case spotlighted the increasing use of federal racketeering charges, which have long been used to combat more traditional organized crime, against violent street gangs.

Federal prosecutors in Maryland recently charged 19 MS-13 members with racketeering counts, the first such cases brought there, after a surge of gang violence. The charges against Alfaro-Fuentes and Reyes were the first time the statutes had been used against MS-13 in Virginia.

Alfaro-Fuentes pleaded guilty this month, making him the first MS-13 member convicted in the Washington region on federal racketeering charges. Reyes, who yesterday became the second, faces a mandatory sentence of life in prison when he is sentenced Dec. 16.

Sandoval and a 16-year-old female companion were shot as they walked in the area of Cavalier Drive and Park Avenue in Herndon. In his plea yesterday, Reyes said he shot both because Sandoval said he was a member of the rival 18th Street gang and because the rules of MS-13 required him to attack rival gang members, prosecutors said. The companion was wounded.

"The messages from this case are clear," U.S. Attorney Paul J. McNulty said. "The federal government will track down and prosecute violent gang criminals wherever they run."

Alan Yamamoto, an attorney for Reyes, said his client felt compelled to shoot Sandoval but didn't mean to hit the girl. "It was absolutely senseless," Yamamoto said.