Marlene LaMar, missing Calif. teen Sierra LaMar's mother, won't give up search for her daughter

(CBS/AP) MORGAN HILL, Calif. - Although Santa Clara police may be convinced that missing high school cheerleader Sierra LaMar is a homicide case, her mother Marlene LaMar still has hope her 15-year-old daughter is alive somewhere and vowed not to stop looking for her.

Photos: Arrest made in case of missing Calif. teen

"I'm not giving up hope. Her body hasn't been found," Marlene LaMar said at a news conference on Tuesday. "I believe there's a reason why she wasn't found."

Santa Clara County Sheriff Laurie Smith said there was "direct and circumstantial" evidence that led investigators to believe that 21-year-old Antolin Garcia-Torres kidnapped and killed the Morgan Hill girl who disappeared in March on her way to school, Los Angeles Times reported.

Garcia-Torres was arrested Monday on suspicion of Sierra's kidnapping and murder after authorities said her DNA was found in his red Volkswagen Jetta and his DNA was found inside her bag. As the victim and Garcia-Torres did not know each other, Smith believed the abduction to be a random act of violence.

"We believe this is the worst type of crime, a stranger abduction of a young girl," Smith said.

Investigators found Sierra's cellphone and pink, Juicy Couture-brand handbag with clothing inside along the side of the road within two miles of her home, shortly after she was last seen walking to her bus stop on March 17.

DNA was found on the items in the bag, Smith said. When lab results came in on March 28, investigators identified Garcia-Torres as their suspect and began 24-hour surveillance. His DNA was taken during a previous assault case of which he was not charged.

Garcia-Torres wasn't arrested right away for numerous reasons.

"We needed additional information," Smith said. "We were hoping he would lead us to where Sierra was."

His arrest on Monday came after lab results determined Sierra's DNA was in his car, Assistant Sheriff Pete 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, according to The Associated Press.

After the arrest he called his mother, Laura Torres, and said he needed her to be strong to help take care of his wife and child. Torres said her son was not involved in the abduction and said when she asked him prior to his arrest if he had any contact with Sierra he said no.

Although the body or a weapon hasn't been found, Smith said investigators have "strong facts" indicating that Sierra was murdered.

"These are very, very difficult cases to prosecute - a homicide when you have not found a victim," she said. "But it has been done."

However,  Marlene LaMar isn't convinced that was the fate of her daughter and begged her daughter's suspected killer to "say where she is," Los Angeles Times reported.

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

Complete coverage of Sierra LaMar on Crimesider