A Houston man who beat his 6-year-old son for eight hours until the boy went into a seizure and died has been charged in the child's killing, police said Monday.

Alex Duncan, 34, is charged with murder and his girlfriend, 30-year-old Tammyra Lanette Sampson, who witnessed the beating early Sunday, is charged with injury to a child by omission, police said.

Both defendants are being held on a $50,000 bond.

Tekerrious "T.K." Jackson lived with his mother but was spending the summer with his father, police said.

Saturday night, Duncan was angry because T.K. wouldn't go to sleep so he made the boy kneel with his arms extended in front of him for eight hours, Sgt. Brian Harris said. Whenever T.K. lowered his arms, Duncan delivered a "flurry of punches" to the boy's chest and body as part of what Duncan called "chest boxing," according to the police report.

Duncan refused to allow T.K. to go to the bathroom, and beat the boy after he urinated on himself, according to court records.

Duncan told investigators he beat his son to teach him how to "man up," police said.

Sampson told police that at one point she stopped Duncan from beating his son so she could show him "how to properly discipline a child with a belt," police said. She said she had witnessed other attacks in the past several days.

The child was rushed to the hospital after he appeared to have a seizure. Police said Duncan told investigators the boy's bruising came from attempts to revive him by slapping him and giving him chest thrusts.

Sampson's daughter, an 11-year-old girl who was not named, told police that Duncan forced her to watch the beatings for several days. The girl is now staying with her grandmother, police said.

T.K.'s mother, Lucy Adams, told reporters she would be forever tormented by the fact she let her son go away for the summer to get to know his biological father.

"If I would've known, I swear to God, I wouldn't have ever brought my baby there to begin with," Adams said. "If he was that much trouble, all he had to do was call me and I would've gone and gotten my baby."