In its entirety, the video that captured those moments is "one of the saddest things I've seen," Clark said.
The release of the footage comes a day after police charged Lamar Beatty, 44, with lying to investigators about the murder. Beatty attempted to frame two men for the murder to get out of a drug debt, Clark said.
Long, of South Philadelphia, and her mother, Stephanie, who was visiting from Harrisburg, were making their way home from a shopping trip and a jewelry party around 10:30 p.m.
When they were accosted, they were steps from Amber Long's car, which they had parked near a friend's house along a desolate stretch of North Front Street.
One of the two videos released Thursday shows three men in a dark-colored, newer-model Chevrolet Impala trolling for potential victims on Front Street. The car drives past Long and her mother, then doubles back, making a U-turn at an apartment complex at Brown Street and Front.
In a second video, two men - one tall and bulky, one with a smaller build - wearing light-colored hoodies walk toward Long and her mother with their heads down.
Just as the men pass the women, they turn and grab for their purses.
The bigger of the men snatches Stephanie Long's purse, while the smaller man grabs Amber Long's purse and pulls.
Seemingly startled, Amber Long stumbles toward her attacker, still holding the purse.
"She didn't fight," Clark said.
The video clip police released Thursday ends just before the man fires a shot, point-blank, into Long's chest. The entire video captured that moment and its aftermath. "This man is a coward - to shoot because he couldn't get her purse off quick enough," Clark said.
In the segment of the video that was not released, the men flee down Front Street to where police believe their getaway driver was waiting.
A source who has viewed the video in its entirety said that Long then staggers toward her mother, curling into the fetal position at her feet.
"Her daughter died in her arms," Clark said.
Long, a Williamsport, Pa., native and a Philadelphia University graduate, moved to the city in 2006 to attend school. She had worked for two years at a construction firm and was working to obtain a certification to design environmentally friendly buildings.
Her mother visited her in the city often. In her Facebook profile photo, the two are smiling next to each other.
In the video released Thursday, the men's faces are not visible. But Clark said he was hoping that they will be recognized by their body language, their build, and their gait.
Their car's license plates cannot be made out on video, but the car appears to have two similar-looking license plates on the front and back. Investigators are trying to determine if the Impala could be from out of state or a rental vehicle.
Clark urged the getaway driver to "get in front of this" and speak to police.
The unit was "a little behind the 8 ball," Clark acknowledged, after Beatty wasted nearly 24 hours of the high-profile investigation.
Beatty, of East Germantown, had attempted to frame two men that police initially held for questioning Monday. He had gleaned details about the murder from the news, Clark said.
"Right now, we need a lead," Clark said.
A $30,000 reward - $20,000 from the city and $10,000 from the Fraternal Order of Police - has been offered in the case.
"It's just a tragic thing," said John McNesby, president of the police union. "There's a mother and daughter leaving from a girls' night out, enjoying themselves, and something tragic like this happens. This is something we felt we needed to do."
Unlike a city reward, which is awarded after a conviction, the union's reward will be paid immediately after an arrest is made.
"You bring them in today, tomorrow you're paid," McNesby said.
Anyone with information about the crime is asked to call the Homicide Unit at 215-686-3334.
Philadelphia police have released a surveillance video compilation showing the purse-snatching that resulted in Amber Long's murder. To see the video, go to www.inquirer.com/surveillance