Officers responded shortly before 11 p.m. to a call of "shots fired" in the area of Ridgeway Street and Barjud Avenue, the Pomona Police Department said in a statement.
The officers found a 37-year-old man and a 27-year-old woman, both Pomona residents, suffering from gunshot wounds behind the Perez Market, according to the news release. Paramedics pronounced the victims dead at the scene.
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The woman was later identified by her mother as Valerie Enriquez. Friends identified the man as Hugo Reynoso. Witnesses said they heard nearly 20 gunshots.
"They just came up and ambushed them, shot them both," said Sherri Piedra, the mother of Valerie Enriquez. Piedra said her daughter, who leaves behind a 10-year-old son, wasn't involved with a gang.
"They never bothered anybody," said John Jordan, who knew the Enriquez and Reynoso. "I can't see why someone would do that. It has to be a case of mistaken identity. I just don't get it."
Homicide detectives were investigating the killings, for which a motive is unknown.
"It's just sad. They're just hanging out, sitting on a curb and there was multiple shots. They probably didn't even see it coming," Sgt. Brian Hagerty with the Pomona Police Department explained.
Investigators said surveillance cameras outside the market captured some of the incident.
Enriquez's family said a memorial vigil has been scheduled for 7 p.m. on Wednesday at the scene of the shooting.
Anyone with information about the shooting was urged to call the Pomona Police Department at (909) 620-2085.