FILE: This photo shows Sierra LaMar.FindSierraLaMar.com
This image, obtained by Fox affiliate KTVU, shows 21-year-old Antolin Garcia-Torres.
This photo, released by the Santa Clara County Sheriff's Office, shows a vehicle similar to the one belonging to the suspect.
Authorities said Tuesday they have DNA evidence linking a 21-year-old man to the suspected kidnapping and murder of a California girl in what officials called a "purely random" crime.
Police arrested and charged Antolin Garcia-Torres late Monday in the disappearance of 15-year-old Sierra LaMar, who was last seen March 16 leaving her home in Morgan Hill.
Santa Clara County Sheriff Laurie Smith said at a Tuesday news conference that Garcia-Torres' DNA was found inside a bag belonging to LaMar. The bag was discovered by investigators within a two-mile radius of the girl's home not long after she disappeared.
Smith said authorities have strong evidence to indicate LaMar was murdered, though her body has not been recovered. She declined to elaborate on the kind of DNA evidence that was found inside the bag.
"It’s my belief this was purely random," Smith said. "We believe that this is the worst kind of crime -- a stranger abduction of a young girl."
Garcia-Torres, who also lives in Morgan Hill, was arrested Monday at a nearby Safeway store where he is an employee, Fox affiliate KTVU reported. He was booked into Santa Clara County Jail on one count of murder and one count of kidnapping in connection with LaMar's disappearance.
Garcia-Torres is the owner of the red Jetta that authorities seized last month in their investigation. Smith said Tuesday that authorities also have "physical evidence linking Sierra to his vehicle."
Smith also said that Garcia-Torres had been under 24-hour surveillance at both his home and the Safeway store since March. He was questioned by police Monday for more than two hours, according to KTVU.
Smith also revealed that Garcia-Torres is a suspect in three other assaults on women in the Morgan Hill area. Forensic evidence links Garcia-Torres to at least one of them, Smith said. The alleged assaults occurred about three years ago.
But the family of Garcia-Torres thinks police have the wrong man. His mother, Laura Torres, told the Associated Press that he asked him before his arrest if he had anything to do with LaMar's disappearance, and he said he had not seen or had contact with her.
LaMar, a sophomore at Sobrato High School, has not been seen or heard from since she left her home on the morning of March 16. Authorities believe she was abducted while walking to a school bus stop.
The girl's cellphone was recovered shortly after her disappearance about three-quarters of a mile from her home after police tracked its electronic ping. Police said the last text LaMar sent out was shortly before 7 a.m. the day she disappeared, and it was not a distress text.
The teen's bag also was discovered a couple of miles from her home. A pair of her pants and shirt were found neatly folded inside the Juicy brand bag.
"It was that clothing that was really instrumental in identifying the suspect," Smith said.
The girl's mother, meanwhile, said Tuesday that she is not giving up hope that her daughter will be found alive.
"We continue to pray until she is found," Marlene LaMar said at Tuesday's news conference. "Our search is not going to end. As a mother I'm hopeful. Her body has not been found and that gives me hope."