No criminal charges are warranted in the death of Corey Foster, a 16-year-old boy who went into cardiac arrest while being physically restrained at a residential treatment center in Yonkers, the Westchester County district attorney concluded Thursday after a three-month investigation.

Corey, who was a residential student at the center, Leake & Watts, died about 8 p.m. on April 18 on the floor of the gym as four staff members held him down, using a technique called “therapeutic crisis intervention,” after playing basketball.

Corey was shooting baskets by himself when two staff members began playing against each other at the same basket, according to accounts of a surveillance videotape of the events. After he bumped into them, the teenager grew visibly angry and lunged at one of the staff members. The staff member and three others took him down.

“Witness statements from more than 55 staff members and residents of Leake & Watts were taken and surveillance video from the gym was analyzed and enhanced,” the district attorney, Janet DiFiore, said in a written statement, summarizing a joint investigation with the Yonkers police and the state Office of Children and Family Services. “There was an extensive review of the school, medical records and the autopsy findings conducted by the Westchester County medical examiner. In addition, an independent examination of the medical records and autopsy findings was performed by a cardiologist.