The shooting occurred at the firing range of the Phoenix federal prison, which is the interagency training ground for federal agents in the region, the FBI said.
IRS agents were at the range Friday for “routine training,” the bureau said.
Details of the incident were not made available.
“To preserve the integrity and capabilities of the investigation, details of the ongoing process will not be released. Findings of the FBI investigation will be turned over to the U.S. Attorney’s Office, District of Arizona for review,” the bureau’s Phoenix office said in a statement.
“The FBI’s investigation will be methodical and thorough to address every element of the incident.”