A soldier has been accused of severely beating his 3-year-old stepson on Christmas after the boy's grandparents placed a hidden camera in the child's bedroom and picked up sounds of suspected beatings.

Army Spc. Alfred Gene Bullock, 21, was on leave from the 101st Airborne Division at Fort Campbell, Ky., when he visited his wife's parents near Jamestown, Ky., about 100 miles east of Nashville.

He is charged with aggravated child abuse and was in custody on $50,000 bond. Bullock attended a preliminary hearing Wednesday, and the case is expected to go before a grand jury next week.

His public defender, Paul Crouch, declined to comment. A message left on Bullock's listed phone number was not immediately returned Thursday.

The camera's lens was covered up, but it captured sounds of the alleged beating, said Sheriff Chuck Cravens. A deputy who responded to the home in rural Fentress County shortly after the taping listened to the recording and said he heard the sound of a child being struck 26 times.

"They had it covered up. But the sound picked up and that's what got him caught," Cravens said.

Bullock was arrested at the home and told Deputy Anthony Hinds that he spanked his stepson with a belt and got "carried away and struck (the boy) hard enough to leave marks," according to the arrest report.

Cravens called the recording "very hard to listen to."

Chief Deputy Mike Reagon said the four- to five-minute recording was secretly taped by the grandparents, Tony and Lori Martin, in the bedroom where the child was staying. The grandparents and the child's mother were away at the time.

Phone calls to the Martins' home went unanswered on Thursday.

Reagon said the child had been living with his mother and stepfather in Clarksville. He is now in the care of his mother.

Officials at Fort Campbell said Bullock is an active-duty soldier, but did not give any other details about his service. Many of the 101st Airborne Division's soldiers are currently deployed to Iraq and more are scheduled to go to Afghanistan in coming months.