A man suspected of killing someone he bumped into on a sidewalk outside New York City's main post office has been found dead in Philadelphia, a law enforcement official said Wednesday.

The man was found in the bathroom of an ex-girlfriend's apartment; the death is being investigated as a possible suicide, said the official, who spoke to The Associated Press on condition of anonymity because the investigation is ongoing.

The normally bustling James A. Farley Post Office is across the street from Madison Square Garden and Pennsylvania Station, and just blocks from the Empire State Building.

The security video showed the pedestrians walking toward each other and bumping shoulders on Sunday. Each kept walking for a moment, but then they turned, exchanged words and moved toward each other.

The victim, 20-year-old Christopher Gutierrez of Manhattan, assumed a fight-like stance, and the suspect made a jabbing motion. Then the dying victim slumped to the post office steps. The suspect walked away.

A German tourist also photographed the suspect, who was identified Tuesday by Police Commissioner Raymond Kelly as Sirmone McCaulla, 28. Authorities gave little background about him except to say he had served in the Army.

Philadelphia officials notified police in New York on Tuesday night that the suspect had been found dead.

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