Authorities have arrested a 27-year-old Wauwatosa man in connection with the incident, which took place at about 1:30 a.m. on Sunday.
One witness, Shelia King, described the scene to FOX 6.
I was upstairs at the bingo hall, and then when it was over they told everybody to exit because it was a shooting downstairs. The security guards was there. They dropped like everybody else dropped. They wasn’t too much protecting each other. They were trying but they were scared too. They fell to the floor. The whole casino fell to the floor basically.
In a statement, the casino called the shooting "an extremely isolated event" and praised its security team for an "outstanding" response.