On Halloween night seven years ago, a 20-year-old exchange student from Germany was in the Canal Street subway station around 3 a.m. when three men approached her. One of them allegedly demanded money, placed the butt of a gun to her neck, attempted rape, and then disappeared.

Her case had gone cold, and the assailant, like 50 others in the city, was listed by sex-crimes investigators as John Doe.

Yesterday, prosecutors from the office of the Manhattan district attorney, Robert Morgenthau, announced that DNA samples taken from felons have resulted in a match and the indictment of a John Doe in the sex-assault case. It was the first such indictment in state history.

David Martinez, 47, a career burglar, was three months away from being released from Sing Sing Correctional Facility when he was arrested yesterday and charged with attempted rape, sexual abuse, and robbery in the 1997 case. If convicted, he faces another 15 years to life in prison.

“This case should assure victims that we don’t give up,” Mr. Morgenthau said, adding that forensic experts were able to match Martinez’s DNA with semen samples found on the victim’s jeans. Martinez’s arraignment in Manhattan State Supreme Court was postponed until tomorrow because no attorney was present to represent him.

The victim, whose name is being withheld, has returned to live in Manhattan to work in the financial-services sector. She was surprised and relieved to hear that a suspect has been charged, Mr. Morgenthau said. There have been no other arrests in the attack.

In another John Doe sex-assault case, prosecutors indicted a second suspect yesterday, a homeless Brooklyn man accused of attempting to murder and violently rape a 33-year-old woman more than 10 years ago in Harlem. Authorities are looking to match his DNA with semen samples taken from the victim’s clothing.