A murderer and another violent criminal escaped from a maximum security prison aboard a garbage truck early Tuesday after hiding inside a trash bin, authorities said.

Jimmy Causey, a convicted kidnapper, and Johnny Brewer, a convicted murderer, were involved in cleaning up and feeding other inmates at the Broad River Correctional Institution (search) in Columbia.

The trash truck left at 6:05 a.m. and officials received a tip one prisoner was missing three hours later.

Policy is to have the trash compacted. "If that didn't happen, we are going to determine why," prisons director Jon Ozmint (search) said.

The men were spotted with a woman in her car just outside Columbia (search) around noon, but it was not clear whether she was with them by choice or by force, investigators said.

Causey, 35, was sentenced to life without parole after being convicted of holding a defense attorney and his family at gunpoint and robbing them in 2002. Brewer, 39, was sentenced to life in prison in 1999 for killing his sister-in-law in 1994. A jury spared him from the death penalty.

Neither prisoner had had any serious disciplinary problems, Ozmint said.