31-year-old Maurice Green is now charged with the murder of 81-year-old Marie Buck on Christmas Eve.
Investigators believe Green went to the store intending to kill Buck's grandson, but he overslept. So instead, Green allegedly opened fire on the 81-year-old who was working behind the counter.
"The decedent had a grandson who the suspect believes has something to do with stealing his expensive chain," Clark said. "As a result of that, he was demanding money back from him. He never gave it back to him. He showed up at the store because he thought the grandson was going to be there working. The grandson was not. And very sadly, he shot and killed the grandmother."
Police say Green took just one step inside the store and opened fire.
Buck was shot eleven times in the chest.
Police say Buck's grandson and Green knew each other from the drug trade.
Investigators began to zero in on their suspect through anonymous tips and surveillance video gathered from the neighborhood.
Clark says there is video of Green parking a vehicle and walking down towards the store minutes before the murder. Then they say cameras captured him fleeing the scene after the murder, and getting back into his vehicle and leaving.
Police arrested Maurice Green outside a home at 54th and Berks in Wynnefield without incident.
Sources say detectives did not find the murder weapon. He has more than a dozen arrests for drugs and other crimes over the past decade.
"It's one of the more horrific murders that I've dealt with in nine years," said Clark. "You have an 81-year-old grandmother, defenseless, who is beloved by the community. And to be killed in this manner is just horrific, it's very sad, but we are very happy that we were able to put this to a close in a very short time period."
It was a very emotional scene Thursday night at the viewing of the beloved South Philadelphia figure. Hundreds showed up to pay respects just hours after police announced the arrest of her alleged killer.
In the bitter cold just two nights before New Year's Eve, the long line of mourners snaked around the Baldi Funeral Home on South Broad Street.
"It's the saddest thing I ever saw, especially coming from a woman like her that did everything for everyone," said Jo-Ann Gormly.
For Buck's relatives, news of the arrest is bittersweet.
Her nephew, Wayne Fantozzi, says, "There's a sense of relief. Also a sense of tragedy, that if he would have just went inside and said, 'this is the deal,' she would have gave him the money."
Another viewing will be held for Marie Buck on Friday followed by the funeral.