Most malls have posted signs saying guns are not allowed on their property. This is why shooters go there; that and schools.
However, the most a mall can do to you is ask you to leave if they find out you have a gun. If someone else had been there with a gun, this guy might not have been able to shoot as many rounds as he did. Why don’t people understand that?
Well in that case, the shooter is in some serious trouble now. /s