The four men were arrested in August for allegedly beating the man, who was identified as an employee of Montgomery's Emmediate Credit Solutions who had been fired or quit and came back angry because his final check had not cleared.
Defense attorneys said the man, who has a criminal record, started the fight and that during the melee taunted the others by declaring he was cooperating with the FBI in an investigation.
The men were arrested on warrants signed by Scott Nesbitt of the State Bureau of Investigation, one of the lead investigators of Swallow and Shurtleff.
Both former attorneys general are facing felony charges for what prosecutors say was allegedly "pay to play" fundraising with payday loan, telemarketer and online businesses that are prone to state regulatory actions.
The U.S. Attorneys Office for Utah originally prosecuted the case against Montgomery, his brothers JD and Michael C., and Jeremy R. Ertmann, all of whom worked at Emmediate Credit Solutions.
But the Utah office withdrew, apparently because it had been recused from anything involving the Swallow/Shurtleff investigation. The reason for that recusal was not made public but such actions normally take place when the office has a conflict of interest in a particular case.
The Montgomery prosecution was taken over by Robert Troyer, first assistant U.S. Attorney for Colorado. On Thursday, he asked the court for dismissal of the case.
"I can simply say the decision to dismiss the case was made in the best interest of justice," a spokesman for the Colorado office, Jeffrey Dorschner, said in an email.
The decision was applauded by Cara Tangaro, Robert Montgomery's attorney.
"It was our opinion that there never was evidence to support this charge and we are thankful that the case was sent to Colorado and a prosecutor in a senior position did the correct thing by dismissing the case," Tangaro said in an email.