The attack took place in February, and Mr. Costello sustained serious head injuries. Dunn had apparently planned the attack, and tensions had risen between the two neighbors because Mr. Costello had gotten a new car under a mobility scheme that had been scratched. Dunn had complained about various issues regarding Mr. Costello's behavior at the housing complex in the months leading up to the attack.
Dunn admitted to the murder, and at Chester Crown Court, he was sentenced to life in prison with a minimum tariff of 17 years and six months. The court heard that Dunn had taken a spade from a neighbor's shed, waited for Mr. Costello's wife to leave, and attacked him from behind as he slept on the sofa, striking him three times.
Mr. Costello underwent emergency brain surgery and remained in critical care, partially paralyzed and unable to speak, before passing away on April 20. Mr. Costello's wife described her husband as a "gentle giant" and expressed her profound grief over his loss. Dunn was apprehended by the police at a nursing home in Wilmslow.