A member of the MS-13 street gang admitted Wednesday he took part in the vengeance killing of a 19-year-old mother and the slaying of her 2-year-old son, who began to cry after he saw his mother shot.

Rene Mejia, 18, admitted in federal court in Central Islip to shooting Vanessa Argueta in the head in a wooded section of Central Islip last year. He said he then handed the weapon to two fellow M-13 members, one of whom then shot the toddler, Diego Torres, according to his attorney, Frank Murphy of Sayville, and federal officials. Mejia did not say who fired the other shots.

The two other MS-13 members have been identified in court papers as Adalberto Guzman and Argueta's former boyfriend. The boyfriend, who has not been named, is still sought by the FBI's Long Island Gang Task Force and Suffolk homicide detectives, officials said. The leader of the MS-13 clique, Heriberto Martinez, also was charged.

Mejia said the plan was to kill Argueta for asking that the rival 18th Street gang threaten her estranged MS-13 boyfriend, according to Murphy.

According to court papers, the MS-13 members tried to lure Argueta alone to her death by saying they were taking her to a restaurant. But she insisted on taking Diego along because "she didn't have anyone to watch her son."

Argueta was shot in the head and chest and her toddler twice in the chest, according to U.S. Attorney Loretta Lynch.

Mejia did not say who shot the boy, but papers filed by prosecutors say he was killed after he hugged the leg of one of the three and "began crying."

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"My client took responsibility for what he did," Murphy said after the plea.

Federal prosecutors John Durham and Ray Tierney, who prosecuted the case, declined to comment.

Mejia pleaded guilty to two counts of causing death by the use of a firearm. He faces a life term when sentenced by U.S. District Judge Joseph Bianco.