The Los Angeles Police Department released body-camera footage that showed the moment officers responding to a domestic violence report shot and killed a 19-year-old man carrying what turned out to be an airsoft rifle.
The incident took place in the Vermont Vista neighbourhood of southeast LA on September 17.
Captain Kelly Muniz, from the Los Angeles Police Department, said: "We are still at the very early stages of this investigation, which can often take up to a year to complete."
The suspected gunman has been named as 19-year-old Luis Herrera, who had earlier made two 911 calls requesting police assistance, claiming that his father was drunk and allegedly beating his mother.
Herrera told the 911 dispatcher, "I tried to get involved and now he is attacking me."
Two LAPD police officers arrived at the property at around 1:20pm. As one of the officers approached the front porch, Herrera emerged from the home carrying what appeared to be a black assault rifle.
WATCH: Bodycam Footage *Graphic*
The officers immediately took cover at the side of the property and ordered the man to drop his weapon.
Ms Muniz said: "He did not comply with officers commands and shouldered the rifle and pointed it directly at the officers, resulting in an officer-involved shooting."
Luis Navarrete was identified as the officer who fatally shot Herrera, he has been placed on administrative leave while the investigation continues.
Ms Muniz added: "We do not draw any conclusions about whether the officers acted consistent with our policies and the law until all the facts are known and the investigation is complete."