BOSTON - Authorities say Boston police officers exchanged gunfire with a man who was helping a gunshot victim, killing him.

Commissioner William Evans says officers spotted two men leaving the area in the city's Dorchester neighborhood Friday morning, one of whom was assisting another with a gunshot injury.

Evans says the officers ordered the uninjured man, who was armed, three times to "Drop your gun," before shots were fired. He said it's still not clear whether the injured man had been struck by police gunfire.

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A third victim with a gunshot wound was found in a nearby residence, which police believe the two men had been in prior to the shootout with police.

The Suffolk County District Attorney's office says it's conducting an independent investigation headed by Assistant District Attorney John Verner.