As Mensah went inside, "armed protesters approached the rear door and a single shotgun round was discharged by a member of the group into Officer Mensah’s backdoor," the release continues.
Several other police departments were called to help disperse the crowd, the Journal Sentine l reports.
In a Facebook post, Mensah said he was home with his girlfriend and that the shotgun shell missed hitting him by inches.
Mensah's Feb. 2 fatal shooting of Alvin Cole is still under investigation. The shootings of Antonio Gonzales and Jay Anderson Jr. were deemed justified self-defense by the Milwaukee County District Attorney's Office.
Former Wisconsin Gov. Scott Walker on Sunday tweeted that the mob attack on Mensah is "domestic terrorism" and officials must take action.
Wauwatosa Mayor Dennis McBride said he would be meeting with the police chief and other city officials Monday morning to ensure Mensah is “fully protected and that criminal behavior of this kind will not happen again.