A line of LAPD officers mourned their slain colleague on Wednesday outside the Olympic Division where he worked while a line of relatives and friends entered the Leimert Park home where he lived.
They were remembering 27-year-old Officer Fernando Arroyos.
"This officer died as a result of a street robbery, in an exchange of gunfire," said LAPD Chief Michel Moore.
Added LAPD Officer Luis Interiano: "He wanted to defend his girlfriend, to stop these guys from doing it to anyone else."
Get Southern California news, weather forecasts and entertainment stories to your inbox. Sign up for NBC LA newsletters.
His stepfather said the alleged robbers wanted his gold chain.
The vigil came on the day Sheriff Alex Villanueva announced the arrests of four people.
"We're going to bring some people to justice on that front," he said.
No names or other details were released, and LA County Sheriff Alex Villanueva said he expects to make a more detailed announcement soon.
Villanueva revealed the arrests during a social media announcement.
Arroyos was shot and killed late Monday during a robbery and exchange of gunfire in a South Los Angeles neighborhood.
Three men and two women were detained Tuesday and were being questioned in connection with the shooting. No names had been released at that time.
One of the men detained Tuesday was found on a street Monday night with a gunshot wound to his leg. The investigation stemming from that person led authorities to the other two men on Tuesday.
Arroyos was identified by Moore during Tuesday morning's police commission meeting. Arroyos, an officer with the LAPD for three years, was assigned to the Olympic division, Moore said.
Arroyos’ death was confirmed at approximately 11:37 p.m. Monday. Police said the officer was shot during a robbery at or near 87th and Beach streets in Florence-Firestone.
Deputies responded about 9:15 p.m. Monday to the 8700 block of Beach Street where they found the officer lying unresponsive in the alley with at least one gunshot wound.
According to authorities, a black pickup approached Arroyos and his girlfriend, and three people got out of the truck.
An argument ensued and Arroyos was shot, detectives said. Arroyos exchanged gunfire with at least one of the robbers, Moore said.
It was not immediately clear whether the attackers knew Arroyos was a law enforcement officer.
Deputies took Arroyos to a hospital where he died.
A witness said he heard several gunshots and saw the officer on the ground. The officer was with a woman who was asking for help.
The attackers left the scene in the pickup. A perimeter spanning several blocks was set up as deputies scoured the area for attackers.
Moore said authorities recovered the officer’s handgun and a firearm believed used by a participant in the crime.
"We do believe that we have an officer-involved shooting here, that our officer exchanged gunfire with at least one of these suspects," Moore said. "We do have our officer’s gun, and we have an additional weapon that we believe was responsible for this assault."
"We know that we need the community’s help, but we also have every faith and confidence that we’ll be identifying the person or persons responsible for this terrible act and this grievous loss," Moore said.
While speaking at a Tuesday morning event for the first day LA Unified students returned to campus after their winter break, Los Angeles Mayor Eric Garcetti mentioned the officer and his tragic death.
"Yesterday evening, a young police officer of the Los Angeles Police Department... was in the unincorporated areas of South Los Angeles shopping for a home," Garcetti said. "A first home, I believe, for himself and his girlfriend."
"My heart is broken," Garcetti continued. "Our city's heart is broken, and certainly our LAPD family's hearts all grieve."
Garcetti said he spoke with the officer's mother and stepfather at the hospital where the officer died. Garcetti not identify Arroyos in his speech because at the time other next-of-kin had not yet been notified of his death.
The Los Angeles County Sheriff's Department is taking the lead on the investigation because the incident happened outside the city of Los Angeles, he said.
"This man died a hero trying to defend himself and his girlfriend," Garcetti said.