It happened on Monday around 8:45 p.m. in the 3400 block of G Street in the Kensington section.
Police say 29-year-old Detective Francis DiGiorgio observed a man while at a stop light with his arms extended and his hands together.
Detective DiGiorgio said he believed the man was pointing a firearm at him while yelling. DiGiorgio then shoots him from inside his vehicle striking him in the stomach. DiGiorgio said he thought the man was going to rob him.
The man has been identified by family members as 28-year-old Joel Johnson. They say Johnson has special needs and often begs for change, and doesn't carry a weapon.
Action News has obtained a new image of the detective at the center of the shooting.
Video shows the Johnson walking up the street to several cars. Video then shows Johnson walking up to DiGiorgio's unmarked vehicle and that's when shot's ring out.
He was taken to the hospital in critical condition and is expected to survive.
Philadelphia Police Commissioner confirmed Johnson didn't have a weapon.
"It's not automatically an issue of whether there's a weapon or not. I know for some people they think that's the way it should be - obviously, it's the first thing we look for. But I'm always going to be very candid with you when I know there's not one. So I'm not going to sit here and tell you that we haven't found one, we don't expect to find one," Ross said.
DiGiorgio joined the department in 2011.