I've got a hell good one, drug them, take them out to a random rave party, slaughter everyone there with a weapon of some sort, then place your friends there, firmly grasping the weapon in one of their hands, then fire a bit so the gunshot residue goes on them. Then write a not in their handwriting that says somehting along the lines of "I did it, it was me, and the other people who are here, we did it". Then place the get their finger prints on the pen, and place it in one of their pockets. Then wait a few minutes and report it to the police (once you have changed clothes of course).
Priceless.