You must decide which way to go in each room. If you see anything appear it will give you a clue as to what room you are in. Remember where each person was murdered and in what fashion they have died.
This is an example of the weaons you are looking for. They will not however have a colored box around them to help you find them. There were 8 murders so you will see at least that many weapons...some will be the same...some different. If you don't make it out alive then you will probably see an extra weapon. The items flash for 1/2 of a second every 5 seconds so you must actually look for them in the murder rooms.