I don't know the solution of the following riddle but still want to share it with u. If u know the answer, please free even to guess for that.

Your a top notch detective, you were in your house eating food when suddenly the phone rings. You pick it up to answer it and you find that the power shuts off. You hear a scream coming from the local department store. You rush to get your Sherlock Holmes stuff. You go there to find a dead woman, 2 shell casings, a bloody knife, gun powder, one slit in the woman's head and no holes. This store sells white gloves,guns,knives,powder,and gun clips.This has 6 floors, Floor 1 is home goods F2 is clothing for 'men F3 is men clothing F4 is kitchen supplies F5 are weapons and F6 is misc.There are atleast 20 people in the store and it is 8:35 PM. The cameras aren't operating due to the blackout. You had to pry open the sliding doors.
How would you solve this murder case?