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NEW YORK (AP) -- A chokehold used by a police officer on a New York City man during his arrest for selling untaxed, loose cigarettes last month caused his death, the medical examiner announced Friday, ruling it a homicide.

Eric Garner, 43, a black man whose videotaped confrontation with a white police officer has caused widespread outcry and calls by the Rev. Al Sharpton for federal prosecution, was killed by "the compression of his chest and prone positioning during physical restraint by police," said medical examiner spokeswoman Julie Bolcer.

Asthma, heart disease and obesity were contributing factors, she said. In the video, Garner can be heard repeatedly saying, "I can't breathe!"

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Chokeholds are prohibited by the New York Police Department. Prosecutors on Staten Island are investigating, and Attorney General Eric Holder has said the Justice Department is "closely monitoring" the probe.

A spokesman for Daniel Donovan, the Staten Island district attorney, said prosecutors were still investigating the death and were awaiting a full autopsy report and death certificate from the medical examiner. Donovan will have to determine whether to empanel a grand jury and charge officers in the death of Garner.

The NYPD didn't immediately respond to a request for comment on the medical examiner's ruling. The officer who put Garner in the chokehold was stripped of his gun and badge pending the investigation, and another was placed on desk duty. Two paramedics and two EMTs were suspended without pay. A spokesman for the police union didn't immediately return a message seeking comment.

Police Commissioner William Bratton, who told reporters that the video appeared to show the officer placing Garner in a prohibited chokehold, ordered a top-to-bottom redesigning of use-of-force training in the NYPD in the wake of Garner's death.

But that response hasn't satisfied some, including Sharpton, who in provocative comments Thursday at City Hall called for the officers involved to be charged criminally. He also told Mayor Bill de Blasio that if de Blasio's own half-black teenage son had a different father, he would be a "candidate for a chokehold."

De Blasio said Friday that he wasn't offended by the comments. The mayor spoke before the medical examiner's announcement; he did not immediately comment after the ruling. He has called Garner's death "very troubling."

Sharpton's spokeswoman said Friday that Garner's family would join him Saturday at his National Action Network Harlem headquarters to address the medical examiner's ruling.

Partial video of the July 17 confrontation shows an officer placing a chokehold on the 6-foot-3, 350-pound Garner, who can be heard complaining repeatedly that he can't breathe as at least four other officers bring him down. He then apparently loses consciousness.

The video shows the officer who apparently choked Garner using his hands to push Garner's face into the sidewalk.

Garner's death has also raised criticism of the broken windows theory of policing, a tactic championed by Bratton that posits that cracking down on relatively minor, low-level offenses such as selling loose cigarettes helps suppress more serious crimes. Bratton, with de Blasio's support, has defended the policing tactic despite some calls for it to be discontinued.