From the BBC, news of a mass grave found near the site of a protest over teacher's rights. Protesters were fired upon, resulting in six confirmed dead and fourty three missing after police arrested the survivors. Warrants are out for the mayor and his chief of security in connection with the disappearances, in addition to the twenty two police officers already being held. Going to try and find reports over the initial incident.
http://www.bbc.com/...
Here, is the article on the original protest, which seems to be over hiring practices in the state of Guerrero which they claimed to favor urban candidates over rural ones. Mexico saw some extended protests in September 2013 over a bill seen as threatening privatization of the school system, starting with teacher performance testing. Unsure if it is related to current events.