SANTEE, Calif. -- A registered sex offender is being held on suspicion of murdering a 24-year-old Santee woman who disappeared May 24, but whose body has not been found, sheriff's deputies said Wednesday.

Brittany Monet Hart, a Costco employee, was last seen buying gasoline at a Santee station, and detectives believe she is dead, Lt. Dennis Brugos said.

Robert Steven Carson, 40, was taken into custody on suspicion of murder Tuesday night after detectives found unspecified evidence in his Spring Valley home in the 1300 block of Marie Street, he said.

Investigators identified Carson, whose birthday is tomorrow, as a person of interest after finding cellular telephone records suggesting the two spoke the night she disappeared, Brugos said.

It was unclear how the two might have been associated.

"Talking to family members (of Hart), they've never heard of him," Brugos said. "We're still looking for the victim and the vehicle, and talking to people acquainted with both of them."

Deputies are looking for Hart's dark gray 1998 Ford Ranger pickup, with the license 6M91555. The truck used to be red, which is evident from red paid visible in the door jambs.

"It was so out of character for her to disappear. She's close to her family. When she's late, she would let them know," Brugos said.

Carson, who is also being held on possession of methamphetamine, runs a business out of his home, which he shares with several roommates, Brugos said.

Carson was convicted assault with intent to commit rape, according to the Megan's Law Web site, www.meganslaw.ca.gov.

Investigators believe Hart was in the house and may have died there.

"We don't believe she's alive," Brugos said.

Carson was locked up and denied bail.

Anyone with information about Hart or the pickup should call the sheriff's homicide office at 858-974-2321 or after hours at 858-565-5200 or Crime Stoppers at 888-580-TIPS.