(05-22) 06:51 PDT MORGAN HILL -- A suspect has been taken into custody in connection with the disappearance of Sierra LaMar, the 15-year-old South Bay girl who has been missing since March, authorities said Monday.

Antolin Garcia-Torres, 21, of San Martin was booked at Santa Clara County Jail on suspicion of murder and kidnapping, said sheriff's Sgt. Jose Cardoza. He would not elaborate, but in announcing the murder arrest investigators have all but confirmed that Sierra is dead.

Garcia-Torres owns a red Volkswagen Jetta seized by sheriff's investigators looking into Sierra's disappearance, Sheriff Laurie Smith told reporters. Sierra's body has not been found, authorities said.

"We have probable cause to believe that he committed the kidnapping and murder of Sierra LaMar," Smith said. "We have not found Sierra yet. We're asking the public to continue - please look for her, please find Sierra for us."

Smith declined additional comment Monday night, saying a news conference was scheduled for Tuesday morning. Relatives of Sierra were to be there.

The suspect attended Central High School in Morgan Hill and does not have a serious criminal history except for a 2009 arrest for resisting arrest, KTVU-TV reported. He had worked at a Safeway store on Tennant Avenue in Morgan Hill where he was arrested at about 6 p.m. after authorities had placed him under surveillance.

Even though Sierra's body hasn't been found, detectives decided to arrest Garcia-Torres out of concern for the public's safety, Smith said.

"We don't want anyone else hurt," she said. "We don't want any more little girls taken."

On May 7, sheriff's investigators released a photograph of a red VW Jetta and asked the public if anyone had seen the car around the time Sierra disappeared on March 16. A day later, authorities acknowledged that they already had the car in custody but were still seeking tips.

Cardoza has said that investigators had focused on the car because of witnesses' descriptions and from viewing surveillance video from homes, businesses and buses in Sierra's neighborhood.

The Jetta was seen in the general area of where Sierra lives near Morgan Hill and where her belongings were found after she vanished, Cardoza said.

Her mother, Marlene LaMar, said she last saw Sierra at home about 6 a.m. March 16 before the girl was to leave to catch a bus to school at nearby Palm and Dougherty avenues.

A day later, search teams found her cell phone off the side of the road near Santa Teresa Boulevard and Scheller Avenue, in the opposite direction of the bus stop. The day after that, they found her Juicy Couture-brand purse near Santa Teresa and Laguna Avenue, a short distance from where her phone was found.

Inside were a neatly folded pair of pants, undergarments and a gray San Jose Sharks sweatshirt her family believes she may have been wearing the day she disappeared. DNA evidence found on the clothing linked Garcia-Torres to the case, KTVU reported.

Also found near the bag were Sierra's schoolbooks, Smith said. The purse and books were "wedged between a building and big cactus" or bush, Smith said.

"Hopefully it will bring us closer to Sierra," said Marc Klaas, who heads the KlaasKids Foundation and has organized numerous searches for Sierra.

"What they've said is they've made an arrest, but they haven't said whether they've recovered Sierra," said Klaas, whose 12-year-old daughter, Polly, was kidnapped and killed by career criminal Richard Allen Davis in 1993. "We should be cautious because we don't have proof one way or another" as to whether Sierra is alive, he said.

Dive teams have searched several reservoirs as well as various smaller percolation ponds in the Morgan Hill region. Klaas said a scheduled Wednesday search will continue as planned unless he learns more about the circumstances of the arrest.