Enrique Delgado Garcia was the only one to raise his hand.

Inside the Massachusetts State Police Academy in New Braintree, Mass., about 70 miles west of Boston, instructors needed someone to face the most experienced boxer in the cadet class.

One trainee had already refused, warning that the matchup would be unfair. Instructors sought other volunteers.

Mr. Delgado Garcia, 25, stepped forward. By the next day, Sept. 13, 2024, he would be dead.

A police academy supervisor and three instructors were charged this year with manslaughter in his death.

Three of the four — Lt. Jennifer Penton, the supervisor of the defensive tactics unit at the time, and the instructors Edwin Montanez and David Rodriguez — were arraigned last month and pleaded not guilty. A third instructor, Casey LaMonte, was arraigned on Wednesday and also pleaded not guilty.

His lawyer, Brian T. Kelly, in an emailed statement called Mr. Delgado Garcia’s death a tragedy, one the state has made “worse by scapegoating an innocent state trooper and charging him with a crime he didn’t commit.”

The unidentified cadet who sparred with Mr. Delgado Garcia before his death was not charged in the case, the authorities said.