not sure how i forgot this one, but here's another fun story from the crime scene investigator who came to my school as a guest speaker for my forensics class:

 
We start off with "Mr. X," a middle aged man with a fixin' for asphyxiation, and "Ms. Y," a middle aged victim. Somewhere along the lines, "Mr. X" decides he'd like to give homicide a try. He abducts "Ms. Y" and takes her to a local apartment he was renting at the time. He then proceeds to strangle "Ms. Y" with a wire or piece of cord (home made garrote) and leaves her in the bathtub of his apartment trying to think of what to do with the body.

well, our dear friend Mr X has never been in this situation before. He decides on dissecting the body into smaller chunks in order to rid the body much more discretely. He tries a few items such as a kitchen knife and cleaver, before realizing that cutting through bone is much more difficult than he anticipated. He gives up, cleans up his mess, and flees the scene with "Ms Y" in a black trashbag.

 
this is where the investigation team comes in. As i said, mr x had been smart enough to at least attempt cleaning up, so finding traces of blood was rather difficult. Well, until they introduced a substance called "luminol," which basically illuminates like glow in the dark dust when interacting with base traces of hemoglobin (to learn more, follow this link). When they gave luminol a try on the bathroom wall, nearly the entire wall began glowing blue (when they turned the lights off of course). the bathtub now very visible had previously contained large quantities of blood. They checked the kitchen to find traces of blood on a large array of sharp objects, all of which "mr. x" had apparently used in attempt to dismember ms y.

when they found ms y's body in the river, they noticed many deep cuts at various joints around the body. The original guess was that they were the cause of death, however upon closer examination it was revealed that mr x had not been up to the job as he had originally thought.