Updated

The teenage suspect arrested on suspicion of murder in the disappearance of an 11-year-old California autistic boy is the child's half brother, a person close to the investigation said Thursday.

The person, who was not authorized to speak publicly about the case, told The Associated Press that charges could be filed as soon as Friday against Terry Dewayne Smith Jr.'s 16-year-old half brother, whose name has not been released.

Police found a body matching Terry's description Wednesday in a shallow grave under a tree about 75 feet from the house where he lived with his mother, half brother and other family members.

The boy was reported missing Sunday by his mother, Shawna Smith, and was last seen Saturday evening by his half brother, authorities have said.

A posting on a Facebook page devoted to the search said Terry's family worried he might have wandered off without food, water or special medication.

Authorities said late Wednesday that a 16-year-old male family member was arrested on suspicion of murder but declined to describe how the suspect was related to Terry.

The death was the result of "a domestic issue" at the house, said Menifee police Chief John Hill.

The discovery of the body brought an end to three days of non-stop searching by volunteers and law enforcement officers who combed the scrubby hills around this rural town 80 miles southeast of Los Angeles on horseback, from the air and using bloodhounds.

It wasn't immediately clear whether the body had been stashed near the boy's house the entire time and, if so, how initial searches failed to turn it up.

Riverside County sheriff's Deputy Albert Martinez did not return a call for comment Thursday. Authorities never ruled out the possibility of foul play, he said earlier. Hill declined to answer questions about the search at a news conference Wednesday and provided few details about the case.

The discovery of the body and subsequent arrest was devastating for the hundreds of volunteers who fanned out in 100-degree temperatures to look for Terry since the weekend.

Many skipped work or joined the search after work to check abandoned trailers and campsites in the hills around town and pass out fliers in nearby towns.

Among them was Marisa Bell, who joined the search from a nearby town because her own 9-year-old son has autism and she sympathized with the mother. Her own child is prone to wandering off because of his condition, she said.

With news that an arrest was made, Bell's worry turned to anger.

"The family allowed so many of us to come out and look and to come out and find this little boy," she said. "I said, `Oh God, here is a mom and a little boy just like mine.' Apparently, that just wasn't true."