Image A firearm covered in blood was recovered after the incident. Credit... New York City Police Department

“Regardless of the circumstances,” he said, “this is a crushing blow to any parent.”

But the circumstances justified the shooting, he said, showing a pair of videos. In the first, a figure who Mr. Kelly said was Shaaliver can be seen approaching a group of several men, including one who Mr. Kelly said was Shaaliver’s target.

Shaaliver can be seen raising a weapon and firing three shots, Mr. Kelly said; the group then scatters. A second video, taken around the corner, showed the next moment: the target running fast around the corner in the middle of the street, a bullet flying past him and slamming into a wall on the far side in a puff of smoke. Mr. Kelly said that after the teenager was ordered to drop his gun, he fired again, though it was unclear whether he was aiming for the fleeing man or the officers.

“I think they did what we would expect officers of any experience level to do,” Mr. Kelly said, noting that officers were trained to “shoot to stop,” not simply to wound. He said the shooting officer, who is white, is 26; his partner, who is black, is 27. Shaaliver was black.

The officers had been assigned to the Bronx as part of the Police Department’s Operation Impact, which matches rookie officers with more seasoned ones to patrol areas with especially high crime rates. City officials have credited the program with helping to reduce crime. But it has long drawn suspicion from civil liberties groups, who say flooding crime-ridden areas with officers has also swelled the number of unwarranted police stops, breeding suspicion and antagonism in some communities.