A clerical error allowed the man suspected of killing Colorado’s prisons chief to be released from custody about four years early.

Court administrators acknowledged the error in a statement Monday. They said that in 2008, Evan Spencer Ebel pleaded guilty to assaulting a prison guard. He was supposed to spend four additional years in prison.

A court clerk failed to note that the sentence was supposed to be served after the one Ebel was already serving. As a result, prison records showed it should run at the same time as the 8-year assault sentence Ebel was already serving. He was released Jan. 28.

Ebel was killed in a shootout in Texas on March 21. He used the same gun that was used to kill prisons chief Tom Clements days earlier.