NEW BOSTON, Texas (AP) — A Texas prison inmate has been convicted of capital murder in the 2015 beating death of a guard who was escorting the handcuffed inmate to a cell.

Billy Joel Tracy was convicted Friday in New Boston. The attack happened July 15, 2015, as Corrections Officer Timothy Davison was escorting Tracy from a dayroom back to his cell at the Telford Unit.

The punishment phase begins Wednesday. Prosecutors are seeking the death penalty.

Investigators say Tracy slipped one hand out of a cuff, grabbed Davison's tray slot bar and used it to beat the officer. Such bars are used to manipulate the opening in cell doors at mealtime.

Tracy is serving life in prison for robbery and aggravated assault from Rockwall County. He has several prior convictions for assaults on officers.