What’s the story on this?

Something does not add up in the whole story, if the male driving(husband) was described by his sister in Mexico Daily News as a stickler for following the rules one would think a) he would not be driving thru Petalan or anywhere at 3:30 am in Guerrero and b) he would not run a road block.
Too bad there will not likely be a real investigation and the "community police" ill continue their trigger happy existence. A sad commentary on the State of Guerrero .

There could be a lot of innocent explanations for why the father did something he normally wouldn't do. I'm sure the son will shed more light on the matter to his family.

The only way the matter will not be investigated is if good people do nothing.

The policía comunitaria are normally not trigger happy by any means. They formed because they were tired of the violence and the inaction by the police and other authorities. The problem is some of their groups have been infiltrated, and others are simply taking advantage of the lack of governmental oversight. While I can't vouch for the group in Petatlán, I also have no reason to doubt their sincerity.