US federal officials will review the local police investigation into the death of two colored people by hanging in Southern California.

The U.S. Federal Bureau of Investigation (FBI), the chief prosecutor's office in central California and the US Department of Justice's Civil Rights Division are overseeing the investigation by Los Angeles County and San Bernardino County investigations of the death.

Fuller was spotted hanging from a tree by a passerby at 3:30 am on June 10 at a park near Palmdale City Hall.

Dr Jonathan Lucas, head of the medical examinations office, said there was no trace at the scene of the murder and investigators found ropes and backpacks at the park.

The City of Palmdale issued a statement expressing its support for an independent investigation and three congressmen asked California prosecutor Xavier Becerra to lead the investigation.

Authorities are awaiting Fuller's toxicity test and investigating his medical history.

The San Bernardino County Police Department also said no evidence was found that Harsch, a black man homeless, was murdered.

Tests related to Harsch's death have not been completed, so the exact cause and method of his death have not been determined.

At a press conference hosted by Alex Villanueva, the Los Angeles County Sheriff, attendees criticized investigators in a rush to judge and ask them to consider the possibility of Fuller and Harsch being murdered.

On June 13, more than 1,000 people took to the streets to protest and commemorate the tree where Fuller's body was discovered.

Meanwhile, an online petition calling for an investigation into his death drew more than 200,000 signatures.