gomez trejo and i'm the former prosecutor of the case in mexico. after the boys went missing, civil unrest grew. in december, 100,000 people marched through mexico city to protest their disappearance. in january 2015, the attorney general announced they had found a dna sample that matched one of the missing students. the government said the case was closed and that the dna from the bone in the river matched missing student alexander mora venancio, confirming their account, which they described as "the historical truth". in this official version, the students left the iguala bus terminal in four buses. corrupt local police working for the mayor and a local drug cartel had attacked them and detained the group of 43. cartel gunmen murdered them, burning their bodies at the dump and throwing their ashes into the river sanjuan. for us there is no scientific evidence to establish the official story. whoever knows where that fragment is coming from knows something about where the rest of the remains of the students may be. it holds the key to a lot of inf