Investigating a crime involving twins is difficult. Their DNA is almost identical, photos and videos do not tell them apart, nor does witness testimony help. In Malaysia, for example, brothers who were selling drugs escaped the death penalty. The police officers could not identify which of the twins they had caught red-handed. And in Russia, a man was deprived of his licence and pretended to be his twin brother, whose driving licence he used. But an acquaintance turned him in. We made a selection of such cases from around the world and asked lawyers what techniques would help in investigations.