Evidently it happens. Twins get started in a pregnancy, but one is absorbed into the other ??? and what results is a chimera, an individual with two completely different sets of DNA.
What does this do to the statistics underneath the use of forensic DNA testing?
Obviously, if the DNA matches that left at the scene, a suspect can be placed at the scene even if the individual is a chimera.
But will this nevertheless throw off forensic DNA testing for identification? That is, can we now rule out that an individual is the crook or the source of future child support just because his DNA sample doesn't match DNA left at the scene?
Guess we'll just have renew the search for the old Cloak of Truth, or else learn how to do the Vulcan Mind Meld thing that Spock used to do.