"This was an execution," said Philadelphia Police Homicide Commander Capt. James Clark.
Some neighbors speculated that Rivera's death was related to a Thanksgiving-weekend murder a block away. On Nov. 25, Louis Chevere, 22, was fatally shot on Westmoreland Street near Hancock. Police are seeking Jorge Aldea, 22, in connection with that homicide.
Rivera, 33, had recently spoken with police about that slaying, a close friend said, but had been unable to provide any information. She was killed on the same day the Daily News ran a photo of Aldea in the paper's "Week's Most Wanted" section.
Law-enforcement sources would not comment on any possible links between the murders. They did confirm that Rivera had had a loud confrontation with an unknown man a few days before her death and that the FBI was involved in the investigation.
The slaying of Rivera - plus another murder Monday night and a death yesterday - brought the city's 2012 homicide total to 28, three more than at this point last year but 12 more than in 2010 to date.
Neighbors said Rivera more commonly went by the name Reina Aguirre-Alonso. She was hardworking and generous and had worked in the store for about a year, living in an apartment upstairs. She sent most of her paycheck to her ailing mother in Mexico.
"She was a strong woman, young and beautiful. I don't know why anyone would want to hurt her at all," said Gladys "Pinkie" Martinez, 53. "If you didn't have money for whatever you wanted, she'd say, 'OK, go on, take it. Pay me later.' "
Emily Gonzalez, 20, worked with Rivera last summer. She said Rivera had been robbed at least twice while working at the store, but didn't seem to be afraid at work.
"She never had a day off," Gonzalez said.
Alexi Santiago, 29, said the murder, combined with drug activity and robberies in the area, made him want to move. Already, he said, his son and daughter are not allowed to play outside.
"This has been happening a lot," he said. "They should have a cop here 24 hours a day."