The Dinner Party

You shout, "Whatever you do, do not touch anything in the room!"
They obey you and slowly step into the middle of the room.
The room was filled with a heavy silence.
Now there were only three guests left. Was the killer trying to kill everyone or was their job over? Whatever it was, you knew you had to find them fast.
You suddenly recognized a boot print next to the door of the cabinet.
What should you do next?