James Martin was sentenced to 20 years behind bars on Tuesday for the 1998 rape and murder of a 14-year-old girl, prosecutors said. View Full Caption DNAinfo/Eddie Small

THE BRONX — A serial killer already locked up for murdering his wife will serve an additional 20 years behind bars after pleading guilty to the 1998 rape and murder of a 14-year-old Bronx girl.

The bruised body of teenager Marleny Cruz was found almost 20 years ago on Feb. 23, 1998 in University Heights on Valentine Avenue after she had been strangled and sexually assaulted, according to the Bronx District Attorney's Office.

The DNA of James Martin, 44, was found on Cruz's fingernails in 2011, and Martin pleaded guilty to manslaughter in her death on Oct. 27, the Bronx DA's Office said.

"He remembered how he started to hit her," said Senior Homicide Counsel Nancy Borko, who prosecuted the case. "They got in an argument, and he threw her to the side against a wrought iron fence like a piece of garbage, never looking back, never to see the injuries he caused."

Martin was sentenced to 20 years behind bars for the crime on Tuesday, and although the victim's cousin Socrates Acevalo said it was difficult to see Martin in court, he was also relieved that Martin will finally be punished for her death.

"Now I can look at her picture and just know that justice was served for her," he said.

Martin is already incarcerated for strangling and killing his wife in 2005 and has 29 years remaining on his sentence for that crime. He's also been connected to the murder of a 15-year-old boy, prosecutors said.

He will not begin serving time on his 20-year sentence for Cruz's death until his sentence for murdering his wife is complete, according to court officials.

Detective Malcolm Reiman of the Bronx Homicide Squad said Martin meets the criteria for a serial killer, and they are investigating whether he is responsible for more crimes.

"There's a great measure of satisfaction with this case," Reiman said. "I think the family and the loved ones are very satisfied with the outcome, and I think that justice was served, and I’m glad to be a part of that."

Martin appeared in court in handcuffs and an orange jumpsuit, and when asked if he had anything to say, he simply replied "No."