MEXICO CITY (Reuters) – Mexican authorities in the violence-plagued southwestern state of Guerrero said they were investigating a gruesome massacre that took place in a part of a remote desert where two rival criminal groups have been fighting for control. Police investigators had found five burned bodies stacked onto a burned vehicle when they arrived in Buenavista de los Hurtado on Friday, the state attorney general said in a statement shared late on Saturday. Citing footage shared by alleged members of the Familia Michoacana on social media and interviews with unnamed sources in the area, l…