ST. LOUIS (KTVI) – The appalling execution-style killing of a St. Louis man has left local residents concerned for the future of their city.

“It was crazy, man, it was most definitely tragic,” downtown resident Tiger Jackson said after seeing footage of the shooting, which was captured by a witness on Monday morning.

The disturbing video has been viewed and shared millions of times on social media.

The clip shows the victim sitting on a curb in front of the St. Louis Globe-Democrat building while the suspect stands over him, apparently struggling to load a gun. The gunman then shoots the victim in the head, to the shock of the witness recording from inside a nearby building.

Police identified Deshawn Thomas, 23, of south St. Louis, as the gunman. The victim was a man named David Saldana, whom police said was homeless.

The two men had previously been involved in an altercation at a Shell gas station, after which Thomas shot Saldana in the back, according to court documents filed by police. Then, as Saldana sat on a curb, begging for his life, Thomas fired the fatal shot, police said.

In addition to the witness video, the crime was also captured by nearby surveillance cameras.

St. Louis resident Marcus Powell lives a couple of blocks away from the scene of the crime. On Tuesday, he said he felt the need to visit the scene, to somehow make sense of things.

“It’s frightening. It makes me afraid for what’s going on in the country and afraid for what’s going on here in St. Louis,” he said.

Tiger Jackson said he knew both Thomas and Saldana, claiming Saldana struggled with mental issues but was harmless.

“It’s getting worse,” Jackson said. “[Thomas] didn’t care what he did. His intention was only to kill, so, there it was.”

Powell and Jackson, too, said they felt an ongoing lack of police presence in the city, especially downtown.

“It just makes me wonder what could possibly happen to me or people that I know, people in my family,” Powell said. “I’m from St. Louis. I like St. Louis. I think it’s a great city.”

Police apprehended Thomas about six blocks from the scene of the crime, as he attempted to enter the main branch of the St. Louis Public Library. He has been charged with first-degree murder and jailed without bond.