A former Los Angeles County sheriff’s deputy convicted and sentenced to death for murder died in custody Thursday, according to the California Department of Corrections and Rehabilitation.

Stephen M. Redd was pronounced dead after prison staff found him unresponsive in his cell at San Quentin Rehabilitation Center, where he’s been incarcerated since 1997. He was 78.

His cause of death remains under investigation.

Redd was sentenced to death after being convicted in 1997 of first-degree murder, first-degree robbery, second-degree burglary, second-degree robbery and attempted murder.

The sentence stemmed from a robbery Redd committed at a Yorba Linda supermarket in 1994.

During the robbery, Redd shot and killed the store’s manager, 34-year-old Timothy McVeigh. Redd evaded arrest for eight months before he was arrested in San Francisco.

Redd’s death sentence has been suspended since 2006, the year California last executed a prisoner. Gov. Gavin Newsom signed a formal moratorium on the death penalty in 2019.