A Michigan man accused of killing six people during a violent, weeks-long crime spree was a police informant who was kept out of prison at the request of a federal law enforcement agency, authorities announced Wednesday. “This is a horrible tragedy. We are going to do everything in our power to get to the bottom of this matter,” U.S. Attorney Matthew Schneider said in a statement. “Kenyel Brown was a law enforcement informant for a period of time, and we have—and currently are—working closely with our law enforcement partners to determine exactly what happened.”

Brown served as a federal informant for the Bureau of Alcohol, Tobacco, Firearms, and Explosives before being handed over to the Detroit Police Department last October, Detroit Police Chief James Craig said at a news conference Wednesday. Despite racking up a slew of federal probation violations while helping the feds, he was allowed to avoid prison at the request of a federal law enforcement agency, a spokesman for the U.S. District Court told The Detroit News. Craig said the department was never warned by the feds about Brown’s long track record of probation violations. “Had we known about his violations, we would have never used him as an informant,” Craig said. Brown is now suspected in six homicides and two carjackings. He shot himself in the head following a police chase on Monday and remains hospitalized in critical condition.