The Marine Corps has concluded an investigation into the death of a Muslim recruit, Raheel Siddiqui, saying that he committed suicide at a training camp where hazing and abuse took place.

A statement said that the investigation had identified 20 trainers at the Parris Island, S.C., camp for possible legal or administrative action — a reflection of the wider investigation that was prompted by Mr. Siddiqui’s death on March 18. Some commanders, senior advisers and drill instructors have already been let go, the statement said.

“Siddiqui’s death was the result of suicide,” a statement said. “Additionally, the investigations revealed departures from the policies and procedures established for Marine Corps recruit training.”

The investigation focused on allegations of abuse and maltreatment at the recruiting depot on Parris Island and found that there was recurrent physical and verbal abuse of recruits by drill instructors, and insufficient oversight.