https://www.azfamily.com/2024/03/01/federal-agent-indicted-deadly-shooting-irs-special-agent-during-training-exercise-phoenix/
According to the indictment, IRS special agents were at a federal firearm range for pistol qualifications and classroom training, whereas Brown, an IRS-CI agent for over 12 years, was a trained Use of Force instructor. After training concluded for the day, Brown and Bauer, who were also trained Use of Force instructors, were in a small building on the gun range known as the “tower,” where instructors observed training.
The shooting happened inside what's called the "tower," an eight-foot by nine-foot building where instructors can observe firearms training.
That’s when prosecutors say, “Brown handled his firearm without due caution and with reckless disregard for human life” and shot Bauer once in the torso. According to the indictment, an IRS-CI agent walked into the tower, where Brown and Bauer were the only ones inside, and that he walked back out to get his cellphone. The agent told investigators that seconds later, he saw Brown run out of the tower yelling, “I f***** up, I shot Pat!”