Credit: Denis Charlet/AFP via Getty An identical twin commits a crime and leaves their DNA at the scene. Can DNA testing reveal which twin is the culprit? This question reportedly came up in a case in France last month, in which the DNA of twin brothers was found on a gun, but conventional DNA testing could not determine which of the brothers it belonged to. The men are monozygotic twins — the result of a single egg splitting in two after being fertilized by a single sperm — meaning they have the same DNA. When DNA is found at a crime scene, forensic scientists typically attempt to identify the person it belongs to using a technique called short tandem repeat (STR) analysis. The technique uses the polymerase chain reaction (PCR) method to amplify up to 30 specific regions of the genome that have a lot of genetic variation, says Brendan Chapman, a forensic scientist and researcher at Murdoch University in Perth, Australia.…