That's when two men approached from behind.
One snatched Stephanie Long's purse. The other went for the bag Amber had picked out with her mother.
Amber held on.
There was a loud pop.
And Stephanie Long turned to see Amber on the ground with a gunshot wound in her chest.
Witnesses nearby would later tell police they heard the mother scream: "They shot my daughter."
Patrol officers arriving on the scene lifted Amber into the back of a squad car, and Stephanie Long cradled her daughter as they raced to Hahnemann University Hospital.
Doctors pronounced her dead 45 minutes later.
On Monday, police had two men "of interest" in custody and believed they were closing in on making arrests. A search warrant was served at a dilapidated house on North Camac Street in the Fern Rock section on Monday night.
Earlier Monday, police had received a tip that there were some people in the home with Stephanie Long's purse and credit cards. They also had a gun.
The two men "of interest" were taken into custody at the house, and police later escorted two women from the house, where broken windows gaped and a screen door sagged from its hinges.
By Monday night, sources said police had interviewed six people.
Homicide Capt. James Clark said the men matched the killers' description.
The two, Clark said, were "very well known to police."
"Hopefully, we'll be able to make an arrest soon," Clark said. "We're still putting some pieces of the puzzle together."
Amber Long was her parents' only child.
A native of Williamsport, Pa., home of the Little League World Series, she moved to Philadelphia for college and ended up staying, working for a local construction firm and moving into a second-floor apartment on a quiet street in South Philadelphia.
She was passionate about art and her architecture degree from Philadelphia University. She was close with her mother, who shared her artistic streak and visited the city often.
In the aftermath of her death, her family was reeling. Her mother stayed inside her daughter's apartment on Ritner Street. Her father, Troy, arrived Monday afternoon to identify her body.
"They are taking it really, really hard," said Berlinda Lancaster, her aunt.
Stephanie Long said Monday afternoon that she could not bear to talk about her daughter's killing anymore.
Lancaster described her niece as a petite and quiet girl with a free spirit, a former gymnast whose artistic bent led her to pursue a degree in architecture.
On Facebook, Amber Long listed herself as a fan of Death Cab for Cutie and Jethro Tull. She posted dozens of photos from a semester abroad in Rome in 2010 - images of the Colosseum, the Forum, the Pantheon.
Her profile photo shows her smiling next to her mother.
"The challenges in life feed into my ambition," she wrote on a LinkedIn profile.
Police remained at the scene most of the day Monday, collecting surveillance footage from a camera posted outside the Urban Youth Racing School, just feet from where Long and her mother were attacked.
Matt Ruben, the president of the Northern Liberties Neighbors Association, described the crime as an "outrage to the sensibility of the community."
"It shatters your peace mind for a time," he said.
He said crime has dropped in Northern Liberties in recent years.
The 900 block of Front Street, spliced by I-95, is still a place where there are "fewer eyes on the street," he acknowledged.
It is not in the center of the neighborhood. It's less populated. And it's bisected by the expressway overpass.
"Development is going on, but it's starting from a place where there wasn't a lot there," Ruben said.
As dusk neared Monday, Barbara Mendenhall, 30, walked her dog past the spot where Long was killed.
She rarely walks alone down Front Street at night. It is desolate, she said. You have to be aware.
Gina Allen, who lives in Liberty Gates, an apartment complex very close to where Long was killed, said that before Sunday night she had felt secure in the neighborhood.
Now, she is shaken.
"It's scary and sad," she said.