The incident happened Sunday morning inside the South Jamaica Housing Development.
Police say the suspect's image was captured on surveillance cameras.
They say he followed a young girl into her elevator where he then sexually assaulted her.
Eyewitness News is told she screamed when the elevator got to her floor and he ran off.
Police blocked the girl's image in the video.
We spoke with one resident who actually recognized the suspect and said he doesn't live at the South Jamaica houses.
The resident then called him on the phone, advising him to get a lawyer immediately.
That tenant let Eyewitness News reporter Lucy Yang listen in on part of the conversation.
The man in the video claims it wasn't an attack, that it was consensual and that he didn't realize how young the girl was.
But police will want to question him themselves.