Interesting concept! Perhaps, instead of revealing the murderer at the end, have some sense of urgency by having the murderer actively track you down. Think of games such as Slenderman and Alien Isolation (and, in a way, Warframe). This can incentivise the player to want to navigate through the house, get the item, and get out before they get caught! Maybe look to other sources of inspiration as well, such as The Blair Witch Project