On the day 43 students disappeared in the southern Mexican town of Iguala, the mayor’s wife was finishing up a speech to local dignitaries on family social services while townspeople waited for a celebratory dance afterward.

Suddenly shots rang out a dozen blocks away and people fled in a panic. Some think the incidents were related, though federal officials said Tuesday they still have no explanation for the Sept. 26 violence that killed six, wounded at least 25 and left so many missing.