SAN DIEGO -- A convicted sex offender suspected of kidnapping an 8-year-old girl from her Nevada home is believed to be in Tijuana, authorities said Tuesday.

Fernando Aguero's mother confirmed that relatives had seen him in Tijuana, and she told detectives she would try to have him contact them, said dispatcher Amanda Ortiz of the sheriff's office in Lyon County, Nev.

Aguero is said to be the live-in boyfriend of the girl's mother and a registered sex offender in California, according to the Lyon County Sheriff's Office.

The California Highway Patrol issued an Amber Alert on Saturday based on law enforcement reports that the kidnapper who snatched Lydia Rupp from her home in Fernley, Nev., brought her into San Diego County.

CHP Officer Alicia Contreras said Tuesday the Amber Alert is still in effect because law enforcement officials believe Aguero could move back and forth between Mexico and San Diego County.

Rupp is Latina, has brown hair, brown eyes and scars on her cheeks. She weighs 85 pounds and is 4 feet 9 inches.

Aguero, a Latino, has silver-grey hair, a moustache, scars on both arms, and a large scar on his lower right leg and foot.

The CHP said Aguero was last seen in San Diego County over the weekend driving a bluish silver 2001 Kia Rio with paper plates that say Reno Mazda Kia.

Anyone who sees the pair is urged to 911 or the Lyon County Sheriff's Office at (775) 463-6620.