Juan Jose Diaz, 24, had been with the LAPD for two years and was most recently assigned to the department's Professional Standards Bureau.
"Officer Diaz was a dedicated public servant and Angeleno that put service to others above all else," the department said on Twitter. "The void his loss leaves within our ranks will not soon be filled."
The Associated Press, citing an official briefed on the investigation, reported that Diaz was out with his girlfriend and two other men at a taco stand in the Lincoln Heights neighborhood of Los Angeles when he noticed man vandalizing something nearby and approached him. The man left, but returned a short time later returned with a group of other males and lifted up his shirt to display a handgun, the official said.
The official added that Diaz and the others tried to get into a car to avoid violence but the man started shooting.
Assistant Police Chief Beatrice Girmala told reporters that a passerby flagged down an LAPD motorcycle officer shortly before 1 a.m. Other officers arrived at the scene and found Diaz and another man suffering from gunshot wounds. Diaz was pronounced dead at the scene, while the second man was hospitalized in unknown condition.
The official told the AP that police believe the gunman is a member of the Avenues gang, which is now the focus of the department's investigation. It is not clear whether Diaz identified himself as a police officer during the initial confrontation with the suspect.
"I don't believe there was any exchange of gunfire," LAPD spokesperson Meghan Aguilar said. "He [Diaz] was targeted, he was murdered. And this was not a run and gun battle of any nature."
"Our hearts break today as one of our officers was murdered while trying to enjoy an evening out with friends," the Los Angeles Police Protective League said in a statement. "We mourn the loss of our brother and we will always remember his service and sacrifice to the Los Angeles Police Department and the residents of our city ... We urge the Chief of Police to utilize every available Department resource to ensure the coward and his accomplices who are responsible for this heinous act are swiftly apprehended and brought to justice."
Chief Michel Moore has asked for the public's help finding the attacker. Anyone with knowledge of the gunman's whereabouts is asked to call 911 or (877) 527-3247
"Words cannot match the depth of sorrow that Angelenos are feeling today," Los Angeles Mayor Eric Garcetti said in a statement, adding: "Our hearts are with Officer Diaz's family and friends. They are experiencing a loss that no one should have to suffer, under circumstances that outrage us all. My promise is that we will hold them close, stand with them every step of the way — and never tire until we find and prosecute the vicious criminals responsible for this horrific tragedy."
The Associated Press contributed to this report.