I get to read New Scientist through my work (under the pretext of looking for new words). In a recent issue, a reader gave the following advice about how to commit a crime:
There is a simpler way for master criminals to throw the police off the scent. If they have blood samples from other people these could be placed at the scene. Or anonymous donor red blood cells could be mixed with DNA amplified from a hair from someone they want to frame to create a blood-like residue. Picking up an ashtray of cigarette stubs from a public place and leaving these at a scene would be the simplest way to create confusing DNA evidence.