New York City's mayor has called video of a police officer using an apparent choke hold while arresting a man who later died "very troubling."
Mayor Bill de Blasio said at a news conference Friday that prosecutors and internal affairs detectives will conduct a "full and thorough investigation."
Police Commissioner William Bratton says the video obtained by the New York Daily News appears to show an officer using a choke hold on 43-year-old Eric Garner.

The department's patrol guide prohibits using the tactic.
Bratton says the man suffered a heart attack and was pronounced dead shortly after he was taken to a hospital.
He says officers were arresting him for selling untaxed cigarettes.

The medical examiner is conducting an autopsy.

 New York City police say the two officers are being placed on modified duty.
Police identified one of the officers Saturday as Daniel Pantaleo. They say he's an eight-year veteran of the force.
Commissioner Bratton says an officer with four years on the job is also being assigned to desk duty while Garner's death is investigated.
Police haven't identified that officer.
The police union called Pantaleo's reassignment a "completely unwarranted, knee-jerk reaction."
Authorities say Garner went into cardiac arrest while being arrested on suspicion of selling untaxed cigarettes in Staten Island.
Video shows the 350-pound Garner becoming irate and refusing to be handcuffed. An officer then places him in what Bratton says appeared to be a chokehold.