LOS ALAMITOS (CBSLA.com) — A Los Alamitos man was shot and killed in broad daylight just yards from his phone, police said Monday.

Investigators believe the victim may have been having trouble with an aggressive neighbor, CBS2/KCAL9’s Jasmine Viel reports.

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Officers were called just after 5 p.m. Sunday and reportedly found Sangju Sung, 39, on the street near Pine and Catalina streets.

Susan Mason lives in the area and says she heard several gunshots ring out. She went outside to find Sung lying in the street.

Mason said she would often wave to the father and husband when he would take his children to the park.

“Mr. Sung was a really sweet man,” said Mason.

Los Alamitos police want to question Sung’s neighbor, Eleazar Vargas, 41, who they say is a person of interest in the case and was in the area at the time of the shooting. They reportedly lived next to each other in the same apartment complex for years and neighbors say there was friction between them.

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Witnesses say Sunday’s confrontation started with an argument in the alley behind the complex and ended on the street, where Sung put his hands in the air.

“This guy put five bullets in him and, when he hit the ground, he stood over him and put in four more,” a witness said.

Mason says Vargas has threatened other neighbors as well.

Police confirm they have been called to this neighborhood before to deal with an unruly neighbor, but they’re not sure if that incident is connected to this shooting.

A man at the scene who identified himself Vargas’ cousin, Sergio, says Vargas is a gentle giant and it was Sung who often threatened his family. He pointed out Vargas’ car was still parked on the street.

The victim’s identity has not been confirmed by police.

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Anyone with information is urged to contact police.