Charging documents say a group of St. Louis police officers gleefully hoped to use unjustified force against protesters in the fall of 2017, assaulted an undercover officer posing as a protester and then attempted to cover it up.

The federal charges made public Thursday against the St. Louis Metropolitan police officers stem from a racially charged period of unrest in the city following the Sept. 15, 2017, acquittal of former police officer Jason Stockley, who is white, in the death of a black man, Anthony Lamar Smith.

Some of the indicted officers are accused of injuring a 22-year veteran police officer who was working in an undercover capacity during the protests. The officer was recording and documenting criminal activity so other officers could lawfully arrest individuals who were committing crimes.

Three officers are accused of throwing the undercover officer to the ground and kicking him, even though he was compliant and not posing a physical threat, the charging documents state.

The officers also allegedly texted about their intent to rough up protesters.

"Let's whoop some ass," Christopher Myers wrote, charging documents say.

Dustin Boone is quoted extensively in the documents:

"It's still a blast beating people that deserve it."

"We really need these ------s to start acting up so we can have some fun."

"It's gonna get IGNORANT tonight!! But it's gonna be a lot of fun beating the hell out of these --------s once the sun goes down and nobody can tell us apart!!!!"

Another officer advised Boone to "have an old white dude as a witness" because there were cameras in the area. "Going rogue does feel good," Randy Hays wrote.

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Officers Boone, Hays and Myers have all been charged with using "unreasonable force." A fourth officer, Bailey Colletta, is charged with joining them in attempting to cover up the crime.

The city says all four officers have been suspended without pay.

Some activists say the messages quoted in the court documents provide insight into the attitudes of some offices toward protesters.

"The text messages confirm our suspicions that these officers were using the anonymity of their SWAT uniforms ... so that they could beat citizens with impunity," attorney Javad Khazaeli said. His law firm has filed suit against police on behalf of nearly two dozen people arrested in protests.

The Rev. Darryl Gray, a black activist who organized many of the Stockley protests, expressed similar opinions of officers' attitudes: "They were going to act out their aggression, they were going to act out their violence, they were going to act out their disregard for the law and the civil liberties and rights of people."

Police Chief John Hayden disputed that belief in a statement, saying the department was "fully cooperative" with the investigation: "I am deeply disappointed in the alleged actions of these individual officers; however, it is in no way reflective of the hard work and dedication exhibited by the men and women of our Department who serve the community on a daily basis with integrity and honor."

Contributing: KSDK-TV; The Associated Press