In Mexico's Culiacan, a city of 1 million residents, an elementary school principal starts each day checking for shootouts before deciding whether to cancel classes.

The murders of about a dozen people in the northern Mexico state of Sinaloa appear to be linked to cartel infighting, something authorities had feared would follow the July 25 detention of two top cartel leaders.

It was surprising when Mexico's most-wanted drug lord landed at an airfield near El Paso, Texas in July.