Mexican authorities found the two children at a different location near where Rodrigo Cervantes Zavala was apprehended, Maricopa County Sheriff Joe Arpaio said at a news conference Monday night.

Arpaio said deputies will fly to Mexico on Tuesday to return the children, both of whom are American citizens, to Arizona to be reunited with their mother.

The children, 18-month-old Bryan Cervantes and 3-year-old Jennifer Cervantes, appeared to be unharmed and were in the custody of Mexican authorities, Arpaio added.

Arpaio declined to provide details of the arrest and the recovery of the children, but said Cervantes Zavala, 34, will be extradited to Arizona to stand trial on murder and kidnapping charges.

The sheriff said information gathered from investigative sources in metropolitan Phoenix led to the arrest, declining to discuss those leads.

"Some of these sources took us to that location," Arpaio said.

A car driven by Cervantes Zavala, a Mexican citizen, was stopped by Mexican officers at the border July 11.

Mexican officers impounded the car as it was crossing the border between Nogales, Ariz., and Nogales, Sonora, because the vehicle didn't have the correct paperwork.

The Mexican border officer didn't recognize that the vehicle was wanted in the case, and the driver and kids were allowed to walk away. Cervantes then took the children in a taxi to a Nogales motel, Mexican authorities have said.

Autopsies on the grandparents -- Saul Lopez Acosta, 63, and Trinidad Castro Acosta, 51-- showed they were each killed by a gunshot to the head, according to the Maricopa County medical examiner's office. The 17-year-old uncle, Jesus Manuel Acosta, was killed by a gunshot to the abdomen. --AP