A police chokehold was directly responsible for killing Eric Garner, and his death two weeks ago in a confrontation on Staten Island was a "homicide," the city medical examiner's office said Friday.

The medical examiner said Garner's asthma, obesity and heart disease brought on by high blood pressure also were contributing factors in his death, which has sparked an uproar over police tactics and a pledge from NYPD Commissioner William Bratton to retrain all police officers on use of force.

Mayor Bill de Blasio, in a statement following the autopsy report's release, said, "As mayor, I remain absolutely committed to ensuring that the proper reforms are enacted to ensure that this won't happen again."

The medical examiner listed the cause of death as "compression of neck (choke hold), compression of chest and prone positioning during physical restraint by police."

Garner, 43, died after police wrangled him to the ground as they tried to handcuff him. One officer, Daniel Pantaleo, was seen on amateur video grabbing Garner around the neck and later pushing his head onto the sidewalk. Garner was heard in the video complaining that he couldn't breathe.

Pantaleo has been placed on modified duty -- relieved of his gun and shield -- and another officer has been put on desk duty while Staten Island District Attorney Daniel Donovan's office investigates Garner's death. Lawyers for Pantaleo couldn't be reached for comment.

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A finding of homicide by the medical examiner means a death was caused by actions of another. It isn't itself a charge of criminal culpability.

Chokeholds to subdue suspects have been banned by the NYPD for more than 20 years.

Garner had been arrested a number of times for allegedly selling loose, untaxed cigarettes, and police said they confronted him on July 17 after local merchants complained about him.

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NYPD's critics, including the Rev. Al Sharpton, accuse police of acting too aggressively against low-level, quality-of-life offenses.

Bratton said in a statement that the NYPD would continue to cooperate with Donovan's office in the investigation.

De Blasio said in his own statement that the city was committed to making changes in police procedures to help "create a culture where the police department and the communities they protect respect each other."

Patrolmen's Benevolent Association president Patrick Lynch cautioned against a rush to judgment and noted in a statement that Garner had "serious health problems."

Lynch also said had Garner not resisted cops' lawful order placing him under arrest, "this tragedy would not have occurred."

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With Matthew Chayes

and Alison Fox