I'm not the only one to consider this; the so-called perfect crime has fascinated thriller writers for a long time, and they've managed to come up with a number of creative ideas, ranging all the way from stabbing people with icicles to stabbing people ... with ... hmmm. Surely they came up with some other options.
Forensics reports that the entry wound was grapey.
But even in the real world, there have been attempts, including successful ones, at committing the Perfect Crime. And, after conducting some research (and all the taping of thousands of magazine articles onto the walls of my creepy little room that entailed), I'm happy to report to you that there seem to be three broad types of Perfect Crime. I present these to you below, along with some historical examples of their usage, and trust you to use this information responsibly, or at the very least, hilariously.