At around 10 a.m. Monday, surveillance shows two men in front of the building at 15th and Locust streets.
One of them goes in and then signals for the other one to follow behind.
Police say they were targeting a 93-year-old woman.
The video shows that once the elderly woman goes past security, seconds later, a suspect in the baseball cap follows behind her, as his accomplice works to distract the security guard at the front desk.
While the guard tries to look up a fictional resident for the second suspect, the first suspect has enough time to walk into the lobby and wait alongside the victim for an elevator.
"Our victim gets on the elevator, selects her floor, our person of interest here selects a floor nine flights above her floor," Philadelphia Police Lieutenant Frank Vanore said.
A third person gets on the elevator as well, but police say nothing happens until she's off and the suspect and the elderly woman are alone.
"When they eventually reach the floor where the victim is about to get off, the robbery does take place on the elevator. He pushes her, he takes money from her, as the doors open, he kicks her, and then throws her off," Vanore said.
Police say the men only got away with $6, but left the old woman with a broken wrist and other minor injuries.
"I just can't believe it, it's happened here. Honestly, I never heard of anything in this building at all," resident Ethan Grindlinger said.
Monday's incident is cause for residents to now look over their shoulder, despite the cameras and security.
"I don't know, now, I'm going to have to think of some kind of protection or something's got to change here, I'm definitely going to start something with the management here," resident Stacey Rosman said.
"These are two cowards, anybody's who's going to pick a 93-year-old woman who's defenseless in this case, we'd really like to know who these individuals are and I'm sure we're going to put a lot of effort into finding them and taking them off the street," Vanore said.
Anyone with information should call Central Detectives 215-686-3093.