SAN DIEGO -- Prosecutors filed additional charges Wednesday alleging a convicted sex offender tried to rape and then used a hammer to kill a Santee woman whose body was found in the Cleveland National Forest three weeks after she disappeared.

Robert Steven Carson, 40, pleaded not guilty June 8 to a murder charge in the death of 24-year-old Brittany Hart, who was last seen buying gas on May 24.

Carson was arrested June 5, based in part on blood that investigators found in the basement of his Spring Valley home, said Deputy District Attorney John Rice.

Hart's decomposed body was found June 15 near Buckman Springs and Interstate 8.

Sheriff's Sgt. Roy Frank wrote in a search warrant affidavit that at least one witness saw a truck similar to the victim's in Carson's neighborhood, and that he was seen with a shovel near the truck.

"Witnesses associated with the case indicated that the suspect had talked about disposing of a human or animal body and using chemicals to assist in concealing or destroying the decedent," Frank wrote.

On Wednesday Rice added a charge of attempted forcible rape against Carson, as well as allegations that he used a hammer in the commission of the killing and the attempted sexual assault.

The defendant is also charged with possession of methamphetamine and committing the crimes while he was out on bail a separate case for allegedly evading a police officer in Coronado and driving under the influence of drugs.

Carson has five felony convictions, including one from 1987 for assault with intent to commit rape against three separate victims. He was also convicted in 1986 of attempted residential burglary, and in 2003 was found guilty of misdemeanor sexual battery.

Carson, who is being held without bail, faces life in prison if convicted of Hart's slaying.

A preliminary hearing is rescheduled for Nov. 27.