Police think up to five suspects confronted the man and woman, and after they exchanged words, one of the suspects pulled out a gun and shot the man.
"I see some guy just laying on the ground, and all this blood and stuff coming out of his mouth, and his girlfriend was crying on the ground," said local resident Shonetish Owens.
The 22-year-old male victim was declared dead at the scene. His identity was not released. The 21-year-old woman was shot in the foot. She was treated at a local hospital and released.
Residents said in the past there had been some gang problems in the area. Police said before shots rang out, the suspects asked the victim where he was from. Police said that usually there is no right answer to that question when gangs are involved.
Residents were shaken by the violence near Monrovia's Old Town, a popular shopping area.
"It scares me, I live a block away," said Monrovia resident Christian Aguedelo.
No suspect descriptions were available. Police hope the female victim will be able to provide more information.
Anyone with information related to the incident was urged to call the L.A. County Sheriff's Department at (323) 890-5500.