A Chicago man who died after police shot him Wednesday night had produced a gun while being chased, prompting officers to open fire, officials said.

Maurice Granton Jr. died of a gunshot wound to the back, according to an early autopsy report, after he refused to stop during a chase, and instead “produced a weapon,” police said. The Civilian Office of Police Accountability, an oversight group, said late Thursday that the investigation revealed early on that three shots were fired from the officer’s gun.

Police spokesman Anthony Guglielmi released a picture of what he says was the gun that Granton produced at the scene, adding that there is evidence that shows that the gun had been fired.

But the suspect’s family said that the firearm wasn’t his.

Kaeinji Jackson, Granton’s sister, told WLS, “No, that’s not his, his [sic] doesn’t have a gun.”

Police involved in a narcotics investigation were surveilling the area Wednesday, and said that security cameras showed Granton taking part in what appeared to be an illegal drug transaction; officers immediately were dispatched to the scene.

Granton was pronounced dead at University of Chicago Hospital.

The Associated Press contributed to this report.