Prior to the arrival of the cousins and yourself, the culprit enterred each of the rooms prior to it being locked. The culprit installed a simple pendulum in each of the victim's bed. When the victim laid down on the bed, the knife would stab the victim in the vitals and kill them instantly. It was easy to make. The beds were airy and much like a balloon. All the culprit needed was some tubing (shaped like a inverted funnel probably) and something sharp, after which pressure would do the rest. The culprit, after setting up a trap in each of these rooms then emptied each toilet of its water. He poured some special preservation fluids into the toilet to fill it halfway or so, after making sure that anything that went down the toilet can be caught and taken out of some piping outside. The culprit then cut his index finger, his middle finger, and his ring finger and inserted one into each of the toilets alive. Some time later, you and the victims arrive at the building. Each victim goes to their respective rooms, locks the door, and locks the window. Each victim goes into the bathroom, and seeing an alive finger in it, flush the toilet to make it "go away". While the finger floats around the edges of the toilet as it flushes, each victim runs out of the bedrooms and jumps onto the bed. The resulting force of their dive into the bed causes the pendulum to push the knife into their body and each victim dies instantly, in the same exact way, all before the toilet finishes its flush cycle and the alive finger goes down the toilet. All three fingers are caught in a bucket outside of the house where the tubing was opened and the culprit leaves the property with all three of his detached fingers and the rest of his fingers.
after some deep soliloquizzing, this is what I came up with. i wish you luck in finding a counter to this... there are a few but it may contradict other truths, hehehe.~
