A Black policeman in the U.S. city of St Louis is to receive a $5-million settlement for injuries received when he was allegedly assaulted by fellow officers while serving undercover during protests in September 2017. 

Luther Hall claimed he was beaten "like Rodney King" after white colleagues mistook him for a protester. The attack happened during a demonstration following the acquittal of a former St. Louis officer who had been accused of fatally shooting a black suspect. 

Hall, a police veteran of more than 20 years, said the beating left him with a facial injury that made it difficult to eat, a tailbone injury and multiple herniated discs in his neck and back, according to a civil lawsuit he filed. 

Several U.S. media outlets said on Tuesday that the settlement agreement was signed by the St Louis mayor and two police executives. 

Two officers have pleaded guilty to federal charges arising from the case and left the city's police force. 

The trial of three others is set to begin on March 15. 

Prosecutors say officers threw Hall to the ground, kicked him and hit him with batons. 

Damning text messages

He told investigators that the officers "beat the f... out of (me) like Rodney King," a reference to the 1991 beating of a motorist by Los Angeles officers. The acquittal three years later of the officers charged in the King assault triggered riots in the city. 

Hall's white police partner at the scene was arrested but not assaulted by police. Undercover officers were tasked with documenting protest activity and property destruction. 

Text messages subsequently obtained by federal agents and carried by local media provided unflattering comments of some officers regarding their response to the protests. 

One officer was quoted as saying, "Let's whoop some ass. The bosses are being a little more lenient with the use of force by us." 

Another said, "The more the merrier! It's going to be fun beating the hell out of these s...heads once the sun goes down and nobody can tell us apart." 

The settlement was welcomed by The Ethical Society of Police, a St Louis law enforcement watchdog group that represents primarily Black police officers. 

"Nothing will make Det. Luther Hall whole again. What he experienced was the epitome of evil from St. Louis City Police Department Officers," the group said. "We hope this settlement will help him heal somehow, and there will be settlements for the citizens who were also brutalized by SLMPD very soon.  

"We also look forward to the officers in Luther's criminal case and other criminal trials from the 2017 protest to be held accountable for their criminal actions."