White Plains police Commissioner David Chong says the shooter was Officer Anthony Carelli. He said his department is cooperating with the Westchester County district attorney's office.
No one has been charged. A grand jury is expected to take up the case next week.
The victim was Kenneth Chamberlain Sr. He was killed after his medical alert pendant went off and police followed an ambulance to his apartment. Chong said at the time that Chamberlain attacked officers with a hatchet and a butcher knife.
An online petition demanding an investigation has gathered nearly 200,000 signatures since the killing of teenager Trayvon Martin in Florida.
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