The notice was filed Tuesday by the family of Dontre Hamilton.
The 31-year-old had been sleeping in a park April 30 when an officer confronted him. A struggle ensued and the officer shot him some 14 times.
Police say the officer was acting in self-defense, but Hamilton's family says police haven't documented their claims that the officer had been beaten in the head.
A message left with the Milwaukee city attorney's office was not immediately returned.
An attorney for Hamilton's family says they're waiting to see the results of the investigation before deciding whether to file a lawsuit.