SOUTH SALT LAKE — A 14-year-old boy who police say is "severely mentally challenged" was found tethered to a couch Wednesday.

Police arrested the boy's uncle, Tai Ngo, the boy's primary caregiver, and booked him into the Salt Lake County Jail for investigation of felony abuse or neglect of a disabled child.

Investigators believe Ngo, 42, would take his disabled nephew to his grandmother's apartment and chain him to the couch during the day while he went to work. One end was tied around the boy's ankle and the other to a couch leg, said South Salt Lake police detective Gary Keller. The boy is "nonverbal," according to jail documents.

The grandmother is apparently very old and not capable of taking care of the boy, Keller said. She was not arrested Wednesday.

A girl who identified herself as a cousin of the boy said the boy was secured with a rope that allowed him to access all parts of the apartment he lived in. The device was necessary, she said, because the boy often chased people in the Harmony Park apartments if he was allowed to go outside.

At the uncle's apartment, police found another chain tied to a couch, Keller said. Detectives believe that when Ngo wasn't using the 6-foot chain, he would lock the teenager in a room "that had nothing in it for extended periods of time," jail records state.

He told police he would "chain up (the boy) by either his ankle or arms when he had things to do," the documents state.

Keller said police did not know how many hours a day the nephew may have been locked up or how long it may have been happening. The abuse accusations surfaced recently after a maintenance man was in the grandmother's apartment, near 3700 S. West Temple, and noticed the teenager chained to the couch.

"We got a report of something weird going on in the apartment," Keller said.

The boy wore a diaper rather than being allowed to use the bathroom, he said.

The teenager and his 12-year-old brother, who is not handicapped, were taken into state protective custody. The boys' mother is unable to care for the children, and their father left some time ago.

Contributing: Joseph M. Dougherty

e-mail: preavy@desnews.com