The St. Louis police chief announced Tuesday that the department would launch a new internal investigation after a jury did not hand down any convictions Monday in the trial of three White officers accused of beating a Black undercover detective during a 2017 Black Lives Matter protest so badly that he had to undergo several surgeries. 

"Officer accountability is, and has been, a pillar of my administration," St. Louis police Chief John Hayden, who is Black, said in a statement released Tuesday. "At the behest of the federal authorities and the United States Attorney’s Office, our Department has delayed any internal investigation into the assault of Officer Hall so as not to compromise the criminal investigation. Our Department has fully cooperated with the federal investigation and has been assured that the FBI will fully cooperate with our internal investigation. It is our hope to now obtain all relevant evidence from the FBI to conduct a complete and thorough internal investigation."

DEREK CHAUVIN TRIAL: DARNELLA FRAZIER, 18, WHO FILMED VIRAL GEORGE FLOYD VIDEO APOLOGIZES FOR 'NOT DOING MORE' 

A federal grand jury on Monday acquitted officer Steven Korte of charges of deprivation of rights under color of law and of lying to the FBI in connection to the attack on Detective Luther Hall. It happened when Hall was mistaken for a protester during demonstrations that erupted after former police officer Jason Stockley, who is White, was found not guilty in the 2011 death of Anthony Lamar Smith, a Black man.

Former officer Christopher Myers also was acquitted Monday of a deprivation of rights count, but the jury could not reach a verdict on a charge of destruction of evidence against Myers for allegedly smashing Hall’s cellphone. The jury also deadlocked on the deprivation of rights charge against former officer Dustin Boone, leading the judge to declare a mistrial on counts where the jury could not agree.

Following a two-week trial, the mixed verdicts were handed down after more than 13 hours of deliberation that first began on Friday, Fox 2 St. Louis reported. Jurors considered text messages between Boone and Myers implicating themselves as participating in the beating at 14th and Olive streets in downtown Louisville the night of Sept. 17, 2017, as well as a livestream taken by Hall while under attack.

But there was no clear evidence showing which officers struck Hall. Defense attorneys argued prosecution was based on speculation, lies and innuendo, both challenging Hall’s ability to correctly identify his attackers. The defense accused the police department of operating under chaos and dysfunction, as officers and supervisors on the street didn’t know undercover officers were working that night.

Prosecutors unsuccessfully objected to the fact that all the jurors selected two weeks ago were White, the St. Louis Post-Dispatch reported. One juror was replaced by an alternate, who is Black, last week.

"St. Louis police beat a Black cop who was working undercover at a protest ‘like Rodney King’ and not one officer was found guilty," Rep. Cori Bush, a Democrat representing Missouri's 1st Congressional District, tweeted after the jury handed down its decision Monday. "If an undercover cop can't get justice, how will the rest of us who have been maced, shot, beaten and brutalized ever get justice?"

MICHIGAN JUDGE DROPS TERRORISM CHARGES FOR 3 MEN ACCUSED IN ALLEGED GOV. WHITMER KIDNAPPING PLOT

The St. Louis region was still recovering from the unrest that followed the fatal 2014 police shooting of Michael Brown in nearby Ferguson. And two nights after Stockley's acquittal, demonstrators broke windows downtown. Police made 123 arrests, but protesters and civil rights leaders said many of those arrested were peaceful demonstrators, journalists and onlookers who were brutalized and taunted.

Hall, who had been recording criminal activity during the protests, became separated from his partner while fleeing officers who were firing pepper-spray pellets and bean bag rounds into the crowd. Hall said he did not push, fight or pull away from the officers because he was stunned. He also testified that he did not say he was undercover because he did not want to ruin his chances of working undercover at future protests. A sergeant later recognized Hall and had him pulled aside.

Assistant U.S. Attorney Carrie Costantin told the jurors that as Hall was complying with orders to get on the ground, he was knocked down, hit, picked up and knocked down again before being attacked with fists, feet and a baton. Hall suffered a hole in his lip that had to be stitched closed, injuries to his jaw, and injuries to his neck that would later require spinal fusion. He also was unable to eat solid food for weeks, causing him to lose 20 pounds.

CLICK HERE TO GET THE FOX NEWS APP

Hall sued the department and officers, including Myers and Boone, but recently settled the case against the department for $5 million.

Two other officers, Randy Hays and Bailey Colletta, both of whom also are White, previously entered pleas in the case. Hays pleaded guilty in 2018 to one felony count of deprivation of rights under color of law and admitted hitting Hall with a baton and shoving him to the ground. Colletta pleaded guilty to making false statements to the grand jury about the assault.

The Associated Press contributed to this report.