Investigators carried out bags of evidence from the apartment as authorities tried to figure out what led to the girl's death.
"Since early this morning there was a whole bunch of cops and police here. We didn't know what was going on but once we saw it was just horrific, like that's not something you would even think could happen," said neighbor Tito Livas.
Police were called to the apartment complex on the 8600 block of Belford Avenue around 11:30 a.m. after the little girl's grandmother found her in the closet of a back bedroom.
"She was found unresponsive by her family members, in need of immediate medical attention. They immediately called the fire department, paramedics, they called us, and unfortunately they were not able to save her," said LAPD Capt. Fabian Lizarraga.
Witnesses said they heard the family screaming for help as they tried to administer CPR before paramedics arrived, all of them desperate to revive the girl.
"I saw a gentlemen who came out crying, his face was pretty much white, without blood, and he was crying, the grandmother wailing and then I saw the body," said witness Del Evano.
The child was rushed to Centinela Hospital where she was pronounced dead. Detectives are awaiting autopsy, which should be performed Friday, to determine exactly how the little girl died.
Friends said the little girl was an only child and say they would often see her playing out in the apartment courtyard.
Described as petite and lively, her tragic death has affected the entire complex.