Officials say, Avion Cotton's autopsy report showed "no signs of physical trauma."
The autopsy did reveal "multiple bags containing a white rocklike substance were found in his stomach and esophagus", according to officials. Preliminary toxicology reports are still pending.
Witnesses said Cotton was choked and maced by officers.
"Officers were telling him, 'Don't resist.' He didn't resist and they pulled him down. He wasn't moving, so I didn't know if he was alive or if he was just laying there and they were choking him, tasing him and he didn't resist and I figured he was dead," said witness Nicki Flowers.
Police said Cotton was chewing on a white substance as he ran from officers were trying to serve a search warrant to a residence in the 600-block of Martin Luther King Jr. Avenue.
The coroner's office says an official cause of death is still pending.
"We have been in close contact with Mr. Cotton's family and our deepest condolences go out to them during this difficult time," said Lake County Coroner Howard Cooper.
The incident is being classified as an in-custody death and at the request of the Waukegan Police Department, it's being investigated by the Illinois State Police.