A panel of independent investigators tasked with probing the 2014 apparent massacre of 43 student teachers in Iguala concluded Sunday that the Mexican government had actively stonewalled its progress. During a press conference, the international experts cast doubt on the federal government’s official story: that municipal police in Guerrero state collaborated with a local drug gang to kidnap and incinerate the victims at a garbage dump. While local police seemed to have assisted in the massacre, the probe revealed, federal police should also be investigated. In addition, the panel suggested, the “incineration” theory is scientifically impossible given the heat required to fully reduce 43 bodies to ash. Since the panel convened in January, they reportedly hit roadblocks with the Mexican government—which claims to have been fully cooperative—including withheld evidence and a lack of access to key potential witnesses.