A California man accused of killing his ex-girlfriend and kidnapping their toddler daughters has been captured and the girls found safe.

Kings County Sheriff David Robinson said Thursday afternoon that FBI agents tracked Jonathan Maldonado-Cruz, using both his cell phone and the victim’s, to Mexico and negotiated his surrender at the San Ysidro border crossing.

The suspect’s mother, he said, played “a critical part” in the negotiations.

Maldonado-Cruz is accused of fatally shooting 22-year-old Madeline Rose Cuevas sometime Monday night or early Tuesday and fleeing with Arya and Alana Maldonado, their 3- and 2-year-old daughters. Police were called by Cuevas’ familywho had been unable to contact her. Deputies found her dead from a gunshot wound.

“The suspect had about a 15-hour head start on us,” Robinson said.

Police issued an Amber Alert for the two children as the search began, as CrimeOnline reported. They were ultimately found in Tijuana, Robins said. The children and the suspect are being brought back to Kings County, where prosecutors are working to determine what charges will be filed.

Joel Cuevas, the victim’s father and the children’s grandfather, thanked the public for their prayers.

”The babies are innocent,” he told KSEE.”Everybody’s prayers were answered. Nothing can bring back my daughter. But my daughter lives in those girls.”