SAN JOSE, Calif. — A man was in custody Tuesday on suspicion of murder and kidnapping after his DNA was found in the bag of a missing girl whose abduction was believed to be a random act of violence, authorities said.

In addition, the DNA of 15-year-old Sierra LaMar was found in the red Volkswagen Jetta of suspect Antolin Garcia-Torres, Santa Clara County Sheriff Laurie Smith said.

The victim and suspect did not know each other, she said.

"We believe this is the worst type of crime, a stranger abduction of a young girl," the sheriff said at a news conference attended by Sierra's family.

Investigators found Sierra's pink, Juicy Couture-brand handbag with clothing and a cell phone along the side of the road within two miles of her home shortly after her mother reported her missing in March.

Garcia-Torres, 21, was linked to the case after his DNA – taken during a previous assault arrest – was linked to clothing found in the bag, authorities said. He was not charged in the previous case.

Garcia-Torres was arrested Monday – more than two months after Sierra's disappearance prompted hundreds of volunteers to turn out for searches and authorities to conduct more than 12,000 hours of investigation.

Sierra was last seen leaving her home in Morgan Hill to go to school on March 16. Authorities believe she was kidnapped while walking to a school bus stop.

Her mother, Marlene LaMar, said the family is holding out hope that the teen is still alive. She pleaded with Garcia-Torres to disclose her whereabouts.

"Please, please give the information that you have to lead us to Sierra to help end this nightmare," LaMar said.

Laura Torres, the mother of Garcia-Torres, said her son was not involved in the abduction. Torres told the San Jose Mercury News that she asked him before he was arrested if he had any contact with Sierra and he said no.

Torres also said her son called her after his arrest and said he needed her to be strong to help take care of his wife and child.

Garcia-Torres, also of Morgan Hill, had been under 24-hour surveillance since March 28. His vehicle was seized on April 7. The DNA evidence used to arrest him also links him to at least one assault in March 2009, Smith said.

The incident involved a Taser, and the victim managed to get away, Assistant Sheriff Pete Rode said, declining to provide more specifics.

Garcia-Torres declined an interview request by The Associated Press, and it was unknown if he has retained a lawyer, said Sgt. Jose Cardoza, a sheriff's office spokesman.

Authorities had other suspects under surveillance while investigating the disappearance of Sierra but focused on Garcia-Torres after he was interviewed several times prior to his arrest at a Morgan Hill supermarket where he used to work, Smith said.

"Right now, we believe he is the only person responsible for the kidnapping and murder of Sierra," Smith said. "These are very difficult cases to prosecute a homicide when you have not found the victim, but it has been done and I think we have adequate facts, in fact, strong facts to believe that she has been murdered."

Marlene LaMar isn't convinced that was the fate of her daughter.

"I'm not giving up hope. Her body hasn't been found," she said. "I believe there's a reason why she wasn't found."

Early in the investigation, a Santa Clara County deputy quickly put together the pieces on the disappearance that helped shape the course of the probe that involved about 100 local, state and federal officers, Rode said.

"He said, `This is not a normal missing child, this is not a runaway, this is not, `She's over at the mall with her boyfriend, she's with a relative,'"' Rode said. "Some instinctive thing just kicked in in him and we went from there."

Garcia-Torres wasn't arrested after his DNA first surfaced in March for numerous reasons, including the possibility that he might lead authorities to Sierra, Rode said.

"At some point, I'm sure he became aware that we were watching him," Rode said, noting that Garcia-Torres was monitored going to work, at home and hanging out with friends.

Garcia-Torres' arrest came after lab results determined Sierra's DNA was in his car, Rode said.

"You don't want to lose him, but at what point in time do you risk having him flee and leave the state and possibly the country?" Rode said. "We did not want to take that chance."

Garcia-Torres could be arraigned as soon as Thursday.

Since Sierra disappeared, volunteers and authorities have searched fields, open spaces and reservoirs near Morgan Hill. The Santa Clara County Sheriff Office announced Tuesday that water searches in reservoirs and water ways in the Morgan Hill area will begin again this week.

Earlier on HuffPost:

View the Help Find Sierra Facebook page.
Loading Slideshow...
  • Sierra LaMar

    Sierra LaMar, 15, vanished after leaving her Morgan Hills, Calif. home on March 16 and headed for school.

  • Sierra LaMar

    Police found LaMar's cellphone on Saturday, March 17 -- the day after she was last seen. Cops said they're searching her phone records for clues.

  • Sierra LaMar

    LaMar was a cheerleader in high school before moving to a new town, Morgan Hill, with her mother in October. Her parents are divorced and police said that both were cooperating with the investigation.

  • Sierra LaMar

    Police are treating LaMar's disappearance as a missing person case. Her parents insist it's unlikely that she ran away.

  • Sierra LaMar

    LaMar is 5-feet-2-inches tall with a thin frame. She was carrying a pink and black Juicy purse when she left home.

  • Sierra LaMar

    Anyone with information about LaMar may contact the Santa Clara County Sheriff's Office at (408) 299-2311

  • Sierra LaMar

  • Peter Robinson

    Deputy Peter Robinson, of the Santa Clara County Sheriff Underwater Search Unit, surveys a pond on Tuesday, April 17, 2012 in Morgan Hill, Calif. The search for missing 15-year-old Northern California girl expanded on Tuesday as investigators followed new leads one month since her disappearance. The Santa Clara County Sheriff's office would not say what the new leads were in the case of Sierra LaMar, except that they came from evidence already collected. The teen was seen leaving her Morgan Hill home on March 16. (AP Photo/Marcio Jose Sanchez)

  • Sierra LaMar

    A sign with a photo of missing teen Sierra LaMar is posted at an intersection on Tuesday, April 17, 2012 in Morgan Hill, Calif. The search for missing 15-year-old Northern California girl expanded on Tuesday as investigators followed new leads one month since her disappearance. The Santa Clara County Sheriff's office would not say what the new leads were in the case of Sierra LaMar, except that they came from evidence already collected. The teen was seen leaving her Morgan Hill home on March 16. (AP Photo/Marcio Jose Sanchez)

  • Santa Clara County Sheriffs underwater search unit

    The Santa Clara County Sheriffs underwater search unit prepares to lower a zodiac into Calero Reservoir to look for clues in the disappearance of missing teenage girl Sierra LaMar Tuesday, March 27, 2012, in Morgan Hill, Calif. LaMar disappeared as she headed out for school on March 16, and her cellphone and bag were found tossed in two separate locations shortly after. (AP Photo/Ben Margot)

  • Sierra LaMar

    HOLD FOR STORY: In this photo from Monday, March 26, 2012, posters bearing images of missing teen Sierra LaMar are seen at Burnett Elementary School in Morgan Hill, Calif. LaMar disappeared as she headed out for school on March 16, and her cellphone and bag were found tossed in two separate locations shortly after. (AP Photo/Ben Margot)