SAN DIEGO -- A rapist already serving a 70-year prison term was charged with murder Monday for allegedly killing two boys in the Palm City area of South San Diego in 1993.

Scott Erskine (pictured, left), 38, was implicated in the killings in March through the use of recently improved DNA-analysis methods, according to prosecutors.

The bodies of Charlie Keever, 13, and Jonathan Sellers, 9, were found two days after they disappeared while riding their bikes on March 27, 1993.

Besides murder, Erskine was charged with the special circumstance allegations of torture, sexual assault and multiple murders.

A decision on whether Erskine will face the death penalty will be made after his preliminary hearing, Deputy District Attorney Paul Pfingst said.

"This is a gruesome case," Pfingst said. "These boys died a horrible death."

Pfingst (pictured, left) said that he decided to charge Erskine after additional testing of DNA material from the crime scene came back to his office on Friday.

"There has probably not been a killing in San Diego County that has influenced more people than the thought of two young boys riding their bikes being sadistically killed in the middle of the day, when boys should be having fun," Pfingst told reporters at an afternoon news conference.

The defendant will be transported from a prison in Lancaster to face the charges in San Diego this Friday, Pfingst said.

The youngsters disappeared while riding their bikes following a weekend lunch at a fast-food restaurant in Palm City. Their bodies turned up two days later on the banks of the Otay River, in an open, brushy area near the end of Saturn Boulevard.

Erskine, who lived in the South Bay at the time of the killings, was linked to the crimes by re-analysis of biological material he allegedly left on one of the boys' bodies during a sexual assault.

The defendant was identified last March as a possible suspect in the crimes through a new statewide DNA database which checks inmates in the state prison system, Pfingst said.

The probability of a person randomly matching the perpetrator's DNA profile is about 1 in 600 billion, according to authorities.

Erskine is serving his prison sentence for raping a woman in San Diego seven months after the boys' killings.

Erskine has a history of assaults dating back 24 years, police said.

"I think all parents in the county were touched by the deaths of two boys, 9 and 13, riding their bikes and having died in this particularly horrible way," Pfingst said.

"If we can bring an end to this nightmare for the families involved -- as well as for the community where these boys lived -- that would be a good thing."