Lawyers for the family of Darrin Hanna said the autopsy found that he died from blunt force trauma as the result of a beating.
A previous autopsy found that a stun gun had been used on Hanna when he was arrested in November.
Wednesday, lawyers said trauma related to the beating triggered Hanna's sickle cell disease.
"It's commonly known that sickle cell can be brought on by trauma. And as result of that trauma he had multi-system organ failure and died," said Hanna family attorney Kevin O'Connor.
More than 80 complaints of police brutally in North Chicago have been made since Hanna's death.