The shooting occurred at a quadplex on the 1600 block of West 205th Street before 6 a.m.
Police said four people, between 20 and 30 years old, were inside the apartment when an argument started and then gunfire erupted.
LAPD shut down several neighborhood blocks as they investigated the quadruple shooting case Friday. Police brought in a team of dogs to sniff out evidence, then obtained search warrants, and began to gather evidence inside the apartment.
"It appears all the individuals inside this location knew each other and that's based on witness accounts," said LAPD Sgt. Rudy Lopez.
"The individuals were inside the apartment when a dispute occurred resulting in shots being fired," said LAPD Cmdr. Nancy Lauer.
A trail of blood led officers blocks away to a fourth person who was shot in the leg and found wounded on Western Avenue and Del Amo Boulevard. The sole survivor is reportedly in fair condition at a local hospital but is not cooperating with detectives.
Luis Enrique Morales who lives next door to the scene said he heard at least nine gunshots around 5:30 a.m. He says he told his wife to call police and made sure his family stayed indoors.
LAPD officials say they aren't searching for a suspect at the moment because they believe this was an isolated incident. Detectives are still sorting out who shot who.
Still, Madison Wood, who also lives next to the scene, says her big concern now is the safety of the neighborhood kids who play outside all the time.
"The kids are out here every day on their bikes, said Madison Wood. "They're playing so it's really scary. It's people like this who are running around and those kids can get in the crossfire."
Homicide detectives scoured the scene and took pictures of surveillance cameras outside nearby homes.
Law enforcement said it would take officials hours to process the massive crime scene.
Neighbors also said they saw cars leaving the scene of the shooting.