Mark Diaz was 19 when he was shot and killed in Holyoke, Massachusetts, on the night of August 26, 2018. Police were called to 256 Maple Street after reports of gunfire and found Diaz inside the residence with a gunshot wound; he was pronounced dead at the scene. A party was underway at the house that evening, with local musicians performing and Diaz among them. Witnesses or investigators say Diaz went outside during the event, was shot on the street, then managed to return inside before collapsing.

The Hampden District Attorney’s Office, Massachusetts State Police Detective Unit and Holyoke Police Department opened a joint investigation. In April 2020 authorities arrested 23-year-old Derrick Brooks of Springfield and charged him with murder; he was ordered held without bail. The investigation remained active after the arrest.

Anyone who attended the party or saw activity on Maple Street that night is asked to come forward with information.