Police say 47-years-old George Batty pulled a knife on Sharon Doyle.
Family members say the Mayfair health food store owner is a former Secret Service agent and Philadelphia cop.
Doyle, 46, was being hugged by relatives late Monday night, relieved that she was unharmed after her harrowing ordeal.
Police say it was just after 5:00 p.m. that the Batty walked into the Stan's Health Food store in the 7100 block of Frankford Avenue.
Moments later, he pulled the knife on the store owner and announced a holdup.
"The perpetrator, point of knife, took the cash register from the counter, threw it on the ground forcibly in order to open it, and started removing money from the cash register," Chief Inspector Scott Small told Action News.
Police say once he had the money in his hands, he pointed the knife against Doyle's chest.
Doyle, according to police, then pulled out her gun and shot the suspect once in his chest.
"When police got here to transport him to the hospital, he still had a $100 clutched in his left hand," Small said.
He was taken to Aria Health Torresdale where he was pronounced dead just before 6:30 p.m.
Doyle was not injured.
"She called real quick, she said she's fine. She was very calm. We were the ones that were freaking out," Doyle's sister Christine Cutter said.
Sharon Doyle's father Joe Perrello says he always worried about her.
"I would say, 'Sharon, are you going to be okay?' [She would say,] 'Don't worry Dad, I can handle it,'" Perrello said.
Doyle's relatives say she once was an officer for the Philadelphia Police Department, as well as for Lower Makefield and Warminster before joining the U.S. Secret Service.
She decided to open up her own business after getting one too many calls in the middle of the night.
Late Monday night, Doyle spoke briefly about her ordeal after closing up her shop.
"I just did what I had to do to be here," Doyle said.
As for her law enforcement training helping her?
"I think it didn't hurt," Doyle said.
Doyle says she will be open for business Tuesday and hopes her customers will stop by.
Meanwhile, police say Batty is well known to law enforcement; he has a long rap sheet and was recently released from prison.
The store owner was not injured.