Antolin Garcia-Torres, 21, is facing murder charges in what is believed to be a random act of violence.
"We believe this is the worst type of crime, a stranger abduction of a young girl," Santa Clara County Sheriff Laurie Smith said at a news conference.
Shortly after her mother reported her missing in March, LaMar's pink, Juicy-brand handbag was found along the side of the road within two miles of her Morgan Hill home. Police found clothing and a cellphone inside.
Authorities say Garcia-Torres' DNA was found in LaMar's bag, and her DNA was found in the suspect's red Volkswagen Jetta.
Garcia-Torres was arrested Monday - more than two months after LaMar's disappearance. Authorities believe she was kidnapped while walking to a school bus stop.
Police say Garcia-Torres wasn't arrested after his DNA first surfaced in March for numerous reasons, including the possibility that he might lead authorities to LaMar.
LaMar's body has not been found, but investigators say they are certain she is dead. The search continues for her body.
Marlene LaMar said she is not certain her daughter is dead, saying, "I'm not giving up hope ... I believe there's a reason why she wasn't found."