he New York Police Department said Friday it's under investigation for a second restraint-related death, this one involving a drugged, emotionally disturbed man four days before a fatal videotaped chokehold that fueled community outcry and led the department to overhaul its use-of-force training.

The medical examiner's office cited "physical restrain by police" as a factor in the July 13 death of Ronald Singleton, who went into cardiac arrest in an ambulance and died on the way to a hospital. It ruled his death a homicide.

The police department is cooperating with the Manhattan district attorney's office, which is leading the investigation into Singleton's death, a police spokesman said. The district attorney's office did not immediately respond to a message seeking comment.

Police said Singleton became irate and combative while riding in a taxi cab around midnight and fought with an officer on foot patrol after exiting near St. Patrick's Cathedral.

Emergency services officers, called in by the patrolling officer, restrained Singleton and placed him in a protective body wrap, police said.

The medical examiner's office said the 45-year-old Singleton was in a state of excited delirium related to severe intoxication from the hallucinogenic drug called PCP or angel dust. It cited heart disease exacerbated by high blood pressure and thickened arteries, as well as obesity, as contributing factors in his death.

Singleton was to undergo a psychiatric evaluation at a hospital under the police department's protocol for emotionally disturbed people, police said, but the ambulance rerouted to a closer hospital when he went into cardiac arrest. He was pronounced dead on arrival.

Police did not immediately respond to questions Friday about the status of the officers involved in Singleton's restraint. A spokesman for the city's largest police union, the Patrolmen's Benevolent Association, did not immediately respond to a message.

Singleton's death drew little attention at the time. But Friday's homicide ruling thrust it into the category of police-related deaths under scrutiny after the July 17 chokehold death of Eric Garner in Staten Island and the Aug. 9 fatal shooting of Michael Brown in Ferguson, Missouri.

Garner, a 43-year-old father of six who had asthma, could be heard on an amateur video shouting "I can't breathe!" as an officer placed him in a chokehold during an arrest on suspicion of selling untaxed cigarettes. The officer was stripped of his gun and badge after Garner's death.

The Staten Island district attorney is assembling a special grand jury next month to hear evidence in the case.

Police in Ferguson have said the 18-year-old Brown was shot after an officer encountered him and another man on the street and one of the men pushed the officer into his squad car and physically assaulted him. But several witnesses have said Brown was shot when his hands were up. Brown's shooting by the officer has spurred unrest in his community, and federal authorities are investigating.