I've read about this concept in the Riverworld series.
It doesn't end well for them.
Random DNA sprayed around a crime scene would just seem weird. Wouldn't they also have to make it seem real? IE fake blood, saliva, whatever, in the same places it would be found in a crime scene?
Just about every computer on the market today runs Unix, except the Mac (and nobody cares about it). -- Bill Joy 6/21/85