Authorities are still investigating, however, how the weapon made its way from that man to Lamar Moore, who was holding it when he walked into the police station Sunday and wounded four officers before being fatally shot.
Elijah Gayden, who has a 1995 cocaine conviction in Elkhart County, Ind., was charged Tuesday with being a felon in possession of a firearm.
Moore, 38, used that same shotgun last weekend at the police station, Jarrod Marsh, an agent with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, said in an affidavit filed Tuesday.
According to the court filing, Gayden told agents he bought the weapon for $200 from another man last spring. Marsh's affidavit does not indicate how Moore obtained the gun.
"We don't know that (Gayden) gave the firearm directly to him. We're still investigating," ATF spokesman Donald Dawkins said Wednesday.
Gayden appeared in federal court on the gun charge Tuesday and was released. There was no attorney listed for Gayden in his case file, and efforts to reach him at his home were not successful. His next court date is Feb. 9.
Two of the wounded officers one who was shot in the head and another in the back may be released from a hospital this week, doctors said.
Autopsy results released Wednesday found that Moore died from multiple gunshot wounds. Toxicology results hadn't come back and weren't expected for a few more days, said Dennis Niemiec, a spokesman for the Wayne County medical examiner's office.
In addition to how he obtained the gun, much remains unclear about what led Moore to the precinct.
Detroit police have confirmed that he was being investigated in connection with a sexual attack on a minor, but authorities stress they won't speculate on his motive. They noted earlier in the week that he may have been upset about a criminal case involving a relative.
Authorities also now say a fire early Tuesday that gutted the home in which Moore had been living was no accident. Detroit fire Lt. Gerod Funderburg said Wednesday the blaze was intentionally set.
Police are not giving more details about the sexual assault investigation.