The following strategy tips may help you survive Aunt Agatha’s dinner party and win the game:
Minimize the odds of Murder cards being traced back to you. Leave them in rooms with as many and as different players as possible. Leave more than one card in a round only if time seems to be running out.
Maximize the odds of drawing a Murder card. Keep track of which players' cards you may have drawn and visit rooms with players whose cards you have not yet drawn. Also be observant on players trying to avoid rooms you have visited and "shadow" them.
Maximize the odds of a player drawing a Save card and a Murder card or of you drawing a Murder card. For the former, visit rooms with as many and as different players as possible. For the latter, be observant on players trying to avoid rooms you have visited.
Maximize the odds of finding the Room card you need. If you steal from a room, 1 of 2 cards will be what you need if you are alone, 1 of 3 cards if one more player is in the room and so on. If you steal from a player, 1 of 5 cards will be what you need if the player only has one card you need, 2 of 5 cards if the player has two cards you need and so on.
Keep track of which players visited the rooms you visited at the point of the 1st murder. Repeat for the 2nd murder and cross-check your findings. One of the players who visited both murder spots is the Murderer.