A convicted killer who was out of prison for only six months before he robbed a group of teenagers is in trouble again, this time for an alleged assault on an officer at a private prison near Kuna.

Robert Troy Eberley, 47, was transported to the Ada County Jail Tuesday after prosecutors charged him with felony assault of a police officer. Eberley was in the recreation yard at the Idaho Correctional Center on Pleasant Valley Road when a corrections officer told him he was going to be moved to a new facility.

Eberley punched the 34-year-old officer in the face several times, causing slight injuries, according to the Ada County Sheriff's Office.

Authorities say the assault occurred July 25, but investigators waited until prosecutors filed the charge to arrest Eberley, which is common for crimes involving prisoners.

"They're not going anywhere," said Andrea Dearden, sheriff's spokeswoman.

Eberley was sentenced to life in prison in Nevada for second-degree murder in 1989, but he was paroled and moved to Idaho in August 2008.

Five months later, he and two men in their 20s were arrested after four teenagers told police they were robbed near the Kuna Caves.

Eberley hit one of the teens in the head with a rock and threatened to assault another while he and his accomplices stole their money and other possessions. He was sentenced in July 2009 to 20 years to life in prison. His fate in prison is not expected to change - the new charge carries a maximum of just five years in prison.

Eberley's next court appearance is Jan. 22 in 4th District Court.