The attack happened June 20 along the 14700 block of Parthenia Street, according to the Los Angeles Police Department.
New video released Friday shows a man in a red shirt running toward the victim and stabbing him while he was on the ground.
Before the incident, authorities say the suspect tried to pick a fight with the victim inside a video store.
"During the fight, the victim's ankle was fractured which caused him to be unable to stand," according to a news release.
The suspect walked away, but then returned with a knife and attacked the already injured victim as he sat on the ground outside, police said. The victim was taken to the hospital in critical condition.
The suspect is described as Hispanic, about 30 years old, about 5 feet, 11 inches tall and 150 pounds, with long brown hair.
Anyone with information about the attack is asked to call Mission Area detectives at (818) 838-9830 or Crime Stoppers at (800) 222-TIPS (8477).