The Chicago Tribune reports that a man has been convicted and sentenced to 76 years in prison for shooting and killing an off-duty police officer. The murder was a result of a scheme to obtain the officer’s gun collection.

A Cook County judge sentenced Bernard Williams, 26, to 55 years for first-degree murder and 21 for armed robbery, says the Tribune. These sentences are to run consecutively, for a total of 76 years, said the state attorney’s office.

The trial jury took less than 3 ½ hours to deliberate before convicting Williams of the crimes. The trial took place in April 2017.

Prosecutors say that David Blake, a Chicago police officer, was dating Williams’ sister at the time of his murder. He mentored Williams and even showed him his massive gun collection he kept in a safe in his south side condo.

Williams’ sister was a witness for the prosecution at his trial, according to the Chicago Sun-Times. Photographs of Williams and his friends posing with Blake’s guns were submitted into evidence. Prosecutors claim that Williams became obsessed with guns after seeing Blake’s collection, and had been vocalizing plans to steal and sell them repeatedly.

Williams was only 18 at the time, and plotted to kill Blake for weeks so that he could steal the guns and sell them.

On November 22, 2010, Williams convinced Blake to drive him to “Dead Man’s Alley,” a secluded spot on the southwest side of Chicago. He then shot Blake in the head six times at close range while inside Blake’s Dodge Durango.

Officer Blake, 45, was one of five officers shot and killed in 2010.

*Photo credit Cook County Sheriff’s Office