When a judge acquitted a white St. Louis police officer in September 2017 for fatally shooting a young black man, the city's police braced for massive protests. But St. Louis Metropolitan Police Department Officer Dustin Boone wasn't just prepared for the unrest - he was pumped. It's gonna get IGNORANT tonight!!" he texted on Sept. 15, 2017, the day of the verdict. "It's gonna be a lot of fun beating the hell out of these s---heads once the sun goes down and nobody can tell us apart!!!!" Two days later, prosecutors say, that's exactly what Boone did to one black protester. Boone, 35, and two other officers, Randy Hays, 31, and Christopher Myers, 27, threw a man to the ground and viciously kicked him and beat him with a riot baton, even though he was complying with their instructions. But the three police officers had no idea that the man was a 22-year police veteran working undercover, whom they beat so badly that he couldn't eat and lost 20 pounds. On Thursday, a federal grand jury indicted the three officers in the assault. They also indicted the men and another officer, Bailey Colletta, 25, for the attack. Prosecutors released text messages showing the officers bragging about assaulting protesters, with Hays even noting that "going rogue does feel good." To protest leaders, the federal charges are a welcome measure of justice - but also a sign of how far St. Louis still has to go.