For Shawna Green and many other residents of Palmdale, a city in California's Mojave Desert, there is no question that Robert Fuller's death was racially motivated.

"In a word, this is a cover-up," said Green, 46, commenting about the 24-year-old black man who was found dead hanging from a tree on June 10.

Authorities initially labelled Fuller's death a suicide, but then backtracked following an outcry from his family and civic leaders who demanded a full investigation and have sought an independent probe and autopsy.

The FBI has now also said it will look into this case, as well as the May 31 hanging death of another black man, 38-year-old Malcolm Harsch, in Victorville -- about 50 miles (80 kilometres) east of Palmdale -- to determine whether both men took their own lives or if there was foul play involved. For many, the two deaths evoke a painful period in US history in the late 19th and early 20th centuries, when thousands of African Americans were lynched in racist extrajudicial killings.

Infamous white supremacist group the Ku Klux Klan was responsible for many of those deaths as they hanged black Americans from trees. The two deaths in California also took place as there are renewed calls for racial justice in the US following the May 25 police killing of George Floyd, another black man, in Minneapolis.

Several vigils and protests for Fuller and Harsch were held in recent days, and on Tuesday more than 200 people gathered again near Palmdale City Hall, where Fuller's body was found, demanding answers. At the base of the tree where he died, dozens of votive candles, bouquets and messages covered the ground. "Stop killing & lynching us," read one sign, while another said: "AmeriKKKa is Lucky Black People want Justice and not Vengeance."

'This is a lynching'

Several people interviewed by AFP dismissed the idea that Fuller could have taken his own life and said they suspected a "lynching" and possible involvement by sympathizers of the Ku Klux Klan. "Black people don't hang themselves," said Dee Johnson, 64. "That's something we don't do. We are not going to repeat history," she added.

Johnson said followers of the Ku Klux Klan had been more vocal in the area since the election of US President Donald Trump, and that more Confederate flags have been seen flying in the region. "They've been coming out more than they ever had," she said, referring to the KKK.

Jamon Hicks, the attorney representing Fuller's family, has criticized local law enforcement for initially moving to quickly close the case. "To rush to the conclusion that this was a suicide and not a homicide is extremely disturbing, especially given the manner by which Mr. Fuller was found -- hanging from a tree," Hicks said Tuesday. "For African Americans in America, hanging from a tree is a lynching."

Fuller's sister Diamond Alexander said he was someone who loved life and was "street smart." "My brother was not suicidal. My brother was a survivor," she said at a vigil over the weekend.

Tommie Anderson, a close friend of Fuller, has described him as "the sweetest person you know," and said he would never have been out at 3:40 am, the time he was found by a passerby. A complete autopsy was performed on June 12, but authorities said they are awaiting toxicology results and are looking into Fuller's medical history before releasing their findings.

Investigators are also conducting a forensic exam on the rope from which he was found hanging and on how it was tied. They are also analysing Fuller's phone and any available surveillance video. The family and residents in Palmdale, about 62 miles (100 kilometres) north of downtown Los Angeles, are eagerly awaiting the full results of the probe.

The desert city -- primarily known for being home to a number of aerospace engineering companies including Boeing and Lockheed Martin -- is a majority-Hispanic community of nearly 170,000, with about 12 percent black residents.

"This is 2020, targeting African Americans is getting old," sighed David Tucker, a minister from south Los Angeles who spoke at the vigil on Tuesday. "Being a black man, I have a target on my back. I'm afraid when I see a police car," said Tucker, adding that his great-great-grandfather had marched with Martin Luther King Jr. during the civil rights movement. "With all the killing, I could be next, easily."