UPDATED, 6 p.m. ET to reflect information from the St. Louis County Police.

A police officer has been removed from his post after he pointed his gun at a group of people documenting events in Ferguson on Tuesday night and threatened to kill them, St. Louis County Police spokesman Brian Schellman told Mashable.

"On Tuesday, August 19, 2014, shortly before midnight, an incident occurred wherein a St. Ann police officer pointed a semi-automatic assault rifle at a peaceful protestor after a verbal exchange," Schellman wrote in an email. (St. Ann is a St. Louis suburb not far from Ferguson.) "It was at this time a St. Louis County police sergeant walked over and immediately took action, forcing the officer to lower the weapon, and escorting him away from the area."

The St. Ann police officer involved in the incident has been relieved of duty and suspended indefinitely, Schellman added, satisfying a request the ACLU sent to the Missouri State Highway Patrol Wednesday afternoon requesting they do just that.

Schellman called the entire incident "inappropriate" and said it was "not indicative of the officers who have worked daily to keep the peace" in Ferguson.

In video footage posted to YouTube, a citizen journalist using live-streaming website Ustream to document the protests in real-time walks with a crowd of protesters and other media when a police officer approaches with his gun raised.

"My hands are up bro, my hands are up," the livestreamer, known as "Rebelutionary Z," says.

"I will fucking kill you," the officer replies. "Get back! Get back!"

Someone in the group asks, "You're going to kill him? What's your name, sir?" The officer replies: "Go fuck yourself."

He then taunts the officer: "Your name's 'Go Fuck Yourself'? All right, 'Go Fuck Yourself.' Hello Officer 'Go Fuck Yourself!'"

Another in the crowd yells out: "Officer 'Go Fuck Yourself' just threatened to kill me!"

A second police officer then approaches the unnamed police officer with the new, unfortunate nickname and pushes his gun away from the crowd while escorting him away.

In a second video recorded during the first incident, journalist Caleb-Michael Files tells the officer to "put the fucking gun down." He refuses.

Mashable's Amanda Wills and Ashley Codianni encountered the officer earlier on Tuesday night when police attempted to corral journalists behind the lines into designated media areas.

This "officer go fuck yourself" guy was in all our faces last night, telling us to turn off lights on our cameras. #Ferguson — Amanda Wills (@AmandaWills) August 20, 2014

It was a chaotic scene as they tried to weed out protesters who had embedded themselves with reporters for protection. The officer, at one point, aggressively asked our reporters to turn off the lights on our cameras as the riot police formed a barricade around the area.

The initial video was shared widely on Twitter Wednesday afternoon accompanied by a hashtag: #OfficerGoFuckYourself, with some tweets containing details of an Anonymous "dox" of the officer, complete with his alleged name, age, date of birth, social security number, credit report and phone number. Someone even launched a satirical, critical Twitter account at @ofcgofuckurself.

@Rebelutionary_Z Looks like the #OfficerGoFuckYourself hashtag is really taking off! Thanks for your coverage <3 pic.twitter.com/wgUkm9yr5R — Rachael P (@plussone) August 20, 2014

Earlier on Wednesday, Mashable spoke with a dispatcher at the St. Ann, Missouri, police department, where the officer is rumored to have worked, who said the chief would call us back. Asked if they had gotten lots of calls about the incident, the dispatcher said, "No. You're the first one." He then laughed and said that was a joke — the phone's been ringing off the hook. We're still waiting for a call from the chief.

Amanda Wills contributed to this report from Ferguson, Missouri