An autopsy determined Paul Cannon died from blunt force trauma to the head, said Dennis Niemiec, a spokesman for the Wayne County medical examiner's office. An earlier report suggested the punch may have caused Cannon to choke on his dentures, but Niemiec said the dentures played no role in the death.
The county prosecutor's office received a warrant request, and it was under review, according to spokesman Mark Bernardi, who didn't expect a charging decision to be made Friday. The employee was being held.
Police said Cannon was reportedly causing a disturbance Thursday afternoon at the restaurant on the city's east side and tried to hit the worker, who swung back.
"A verbal argument occurred," police Sgt. Eren Stephens said. "It escalated into a physical altercation."
Jerome Perdu, 59, of Detroit, works as a security guard nearby and said he was at the restaurant at the time. He said he didn't see the customer get hit, but watched as paramedics tried to revive him. The restaurant was crowded at the time, he said.
"I just seen him lying on the floor," Perdu said. "EMS was pumping him."
He died at a hospital, police said. Cannon's last known address was in Detroit, Niemiec said.
Earlier in the day, a sign on the restaurant's door indicated that only the drive-through was open, and a steady stream of customers pulled into the parking lot. A manager who opened the locked door said any comment would come from the fast food company.
Denise Wilson, a spokeswoman for Miami-based Burger King, said the franchise owner was cooperating with Detroit police.
"The safety and security of all guests and crew members is a top priority at all Burger King restaurants," she said in a statement.