Witnesses reported hearing four to 10 shots in the 100 block of E Street in Chula Vista about 7:40 a.m. The victim, whose name was not immediately available, collapsed and died between two parked cars.
"My understanding is that there was a dispute between two neighbors at the complex," police Capt. Lon Turner told reporters.
A neighbor said the conflict could have been over bullying.
"Bullying. I believe because they were little people. I thought they took care of it," said Oskar Vargars.
Oskar Vargas was friends with both the suspect and the victim. Vargas said the issue was between the daughter of the victim's girlfriend and Michael Majerus' daughter.
"Extremely surprised. I did not even know he had guns. I didn't think he was capable of anything like this. He was such a good guy" said Vargas.
The alleged shooter, had been armed with an assault rifle similar to an AK-47, and had locked himself inside an apartment with his wife and two youngsters under age 10.
SWAT officers took up positions around the complex, escorted the dead man's wife and two children from their residence and helped a 93-year-old man in frail health leave, as well. About 3:30 p.m., the suspect allowed police to remove the woman and children from the apartment, though he still refused to surrender, Turner said.
Just under an hour later, a gunshot sounded from inside the unit, police said. SWAT officers then sent in a camera-equipped robot to check on the suspect, finding him dead from an apparent self-inflicted bullet wound about 5:15 p.m.
In all, police cleared 41 adults and 15 children out of the apartments.
As the stalemate continued through the morning and afternoon, authorities were unable to recover the victim's body due to its proximity to the suspected shooter's apartment, according to Turner.
As of 2 p.m., the suspect had resumed talking with the negotiators, at times suggesting that he wanted to surrender but still failing to do so. His wife also spoke with officers before she and the children were rescued.