A Missouri man has been sentenced to prison for the fatal shooting of his grandfather, whom he accused of poisoning him. He later told authorities, “he’ll never do it again.”

Mastin Paul William Raines, who was 19 at the time of the incident, admitted to killing his 55-year-old grandfather, William Mark Gustin, in 2021. Now 23, Raines pleaded guilty to voluntary manslaughter and received a 13-year prison sentence this past Monday, according to court documents.

The incident unfolded on August 1, 2021, when Johnson County Sheriff’s deputies were dispatched to a report of gunfire at a residence on the 300 block of Southwest Highway 58 in Centerview, a small community roughly 55 miles southeast of Kansas City. This information was detailed in a probable cause affidavit accessed by the Warrensburg Star Journal.

Upon arrival, deputies encountered Raines, who reportedly stated, “He will never do it again,” according to the affidavit. When asked by deputies to clarify, Raines allegedly responded, “My grandfather, he’ll never do that again.”

Inside the home, officers discovered Gustin’s body lying on the living room floor, with gunshot wounds to his stomach and neck. Evidence suggested that Raines had shot his grandfather at close range, as the bullets traveled through Gustin’s body and penetrated the floor beneath him.

A witness later told detectives they heard gunshots and saw Raines holding a rifle. The witness hid in the bathroom and later convinced Raines to give up the gun.

After receiving his Miranda rights, Raines reportedly accused his grandfather of poisoning him. He allegedly said that he decided that “Today was the day” and loaded the firearm and began drinking alcohol to gather up the courage to shoot him.

According to his obituary, Gustin owned a construction company.

“He enjoyed spending time in the outdoors, trips to the lake and going to Branson; he especially enjoyed riding his motorcycle,” the obituary said.