The shooting occurred at 2:26 p.m. Sunday in the 11300 block of Hatteras Street, according to Los Angeles police.
Authorities identified the shooting victim as Roberto Fletes, 42, of North Hollywood. Police said he died at a hospital.
After the shooting, authorities say the gunman kidnapped his ex-girlfriend, identified as 31-year-old Jenny Marie Downes.
Police say Downes and the suspect, identified as 37-year-old Shane Winfield Rayment were in an argument near the intersection and Hatteras Street and Tujunga Avenue.
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Fletes tried to intervene and was shot by Rayment, according to police. The alleged gunman then forced his ex-girlfriend into a truck and fled the scene.
A crime alert was issued for Rayment. Also listed in the alert were four people believed to have accompanied by him -- a 30-year-old white man, 5 feet, 9 inches tall, 170 pounds, with long blond hair, blue eyes, a black shirt and blue jeans; and three white female suspects with no further descriptions.
The suspects' vehicle was described as a green four-door pickup, possibly a Dodge Ram.
Anyone with information was asked to contact Valley Bureau homicide detectives at 818-374-1923 or the Department Operations Center at 213-484-6700. Anonymous tips can be left at Crime Stoppers, 800-222-TIPS (8477).
City News Service contributed to this report.