PALMDALE, CALIF. – Poncitlan Square in the center of this high desert city is a tidy expanse of green lawn with a gazebo and a fountain. On one side is City Hall, on the other, a fire station. There is a cafe and the Whispering Palms Apartments. This time last year, for the first time, it was filled with revelers celebrating Juneteenth, the annual holiday to mark the end of slavery.

Today, it is a place of mourning, anger and suspicion after a black man was found dead in the park, hanging from a tree.

Now, the grass around the Chinese pistache tree is buried under balloons, candles, flowers and photographs of the man, Robert Fuller, one in his cap and gown, another with his sisters. A giant American flag flies overhead, as people gather around the tree, absorbed in despair for another black life lost.

The Los Angeles Sheriff's Department first ruled the case a suicide. But it quickly shifted course by vowing a full investigation, a reaction in part to the protests, here and across the country, against police violence and racism.

"Black people don't do that," said Terry L. Scott, a real estate agent from Los Angeles, about an hour's drive west, expressing a sentiment shared by many in Palmdale. "They don't hang themselves from a tree in a public park."

As tensions across the country grow in the wake of the killing of George Floyd, this desert region east of Los Angeles has been shaken not just by the death of Fuller but by a second, similar case, in nearby Victorville, where a black man was found dead, tied to a tree branch with a computer cord around his neck.

That case, too, was first ruled a suicide, and officials in both cases say there is no sign of foul play. But now, in response to pleas from activists and family members, local authorities are promising full investigations. And in a sign of the mistrust between the black community and law enforcement in the two cities, the FBI is monitoring the probes, as are investigators with the state's office of attorney general.

Taken together, the cases highlight not only the moment America finds itself in but also the long and well-documented history in Southern California of racial discrimination, police abuses and the lingering presence of white supremacist groups.

Emotions were already raw over the killing of Floyd and the unrest it provoked, not to mention the accumulated grievances here over years of police abuses. Now, the potent symbolism of black men hanging from trees has put this city on edge — the atmosphere within the black community is a "powder keg," one local pastor said — causing many to question law enforcement's handling of the cases.

"I think it was a rush to judgment," said Jamon R. Hicks, a Los Angeles civil rights attorney hired by Fuller's family who is working to arrange an independent autopsy. "What's so disturbing about that is there's this history they didn't consider. My first thought would not be a suicide. My first thought is, this is a modern-day lynching."

There have been at least three other hangings in public places in recent days that were ruled suicides, in Texas and New York City, sparking anguish and questions. A black teenager was found dead near an elementary school in Spring, Texas. A Hispanic man was found dead in Houston. And a black man was found dead in a tree in a Manhattan park.

Officials in all these cases said there is no evidence they were not suicides. Nevertheless, the deaths have drawn attention on social media, with activists expressing fears they could be signs of a backlash against the Black Lives Matter movement, and others calling for federal investigations.

The families of both Harsch, 38, and Fuller, 24, have cast doubt that their loved ones' deaths were suicides. At a rally in Palmdale recently, Diamond Alexander, Fuller's sister, who lives in Arizona, said, "my brother was not suicidal. He wasn't."

Karmen Smith, a mental health therapist, was so moved by the death of Fuller that she drove from Las Vegas to see the town square.

She said she could not believe a black man would kill himself by hanging on a tree in a public park, given the history in America of lynching.

When Smith walked into the park Tuesday, she said, "I just screamed. I was just so outraged and saddened."