It happened in on Lot Avenue in Brownsville Sunday evening.
They were in the elevator alone.
The teenager in the white coat didn't know it, but he was about to be murdered.
His killer already had the gun in his right hand.
One shot, then another, and another.
The gunfire echoed down the hallway.
The bullets ripped through the victim's body and ricocheted off the tile floor.
Moments later, the suspect walked calmly through the building's front gate.
He bounded down the sidewalk as if a young man were not bleeding to death on the fourth floor.
The victim was identified as 18-year-old Andre Pitts.
The motive was not immediately clear.
Andre no longer lived in the building, and residents said he was visiting a girlfriend at the time of the shooting.
Some young boys, who knew him, passed out fliers with Andre's picture Tuesday.
So far this year, compared to last, murders are down 50% across Northern Brooklyn but not so in the 73rd precinct.
Although rapes are down 36%, robberies are up 12%, burglaries are up more than double that at 26%, and overall crime is up 4%.
Citywide crime continues to decline.
The suspect is described as black man in his 20s, approximately 5-foot-8 and wearing a black jacket with a green hood with green, white and red stripes on the sleeves.
He is also wearing a black doo rag and red sneakers.