Prosecutors revealed Monday which of three suspects arrested in recent months they believe pulled the trigger in a fatal Kirkland House shooting in May.

According to the Boston Globe, Middlesex Assistant District Attorney Daniel Bennett alleged that Jabrai J. Copney, 20, shot Cambridge resident Justin Cosby, leaving the 21-year-old dead just hours later. The news came at the arraignment Monday morning of Jason Aquino, 23, another of the three suspects.

Copney pleaded not guilty to all five of the prosecutor's charges, including first degree murder, at his arraignment in Middlesex Superior Court on July 22.

Bennett said that Copney, Aquino, and Blayn “Bliz” Jiggetts, 19, arrived at Harvard from New York on May 18. Armed with a 9 mm handgun, they met Cosby in Kirkland’s basement to steal $1,000 in drug money. Jiggetts then handed the gun to Copney, who shot Cosby after a struggle, Bennett said.

After Cosby was shot, the three suspects fled to Lowell House—the residence of Brittany J. Smith ’09, who was dating Copney—to hide the gun. Meanwhile, Cosby had stumbled out of Kirkland and collapsed onto Dunster Street. The three then escaped to South Station, where they took a bus back to New York City, Bennett said.

—Staff writer Bonnie J. Kavoussi can be reached at kavoussi@fas.harvard.edu.