MEXICO CITY -- The brazen murder of several family members of a Mexican Naval hero threatens to start a dangerous new chapter in the country's drug war, in which cartels increasingly resort to terror tactics to try to force the government to back off.

More than a dozen hit men carrying AK-47 and AR-15 assault rifles burst into a house in eastern Mexico around midnight Monday, gunning down several relatives of 3rd Petty Officer Melquisedet Angulo, the 30-year-old who was hailed as a national hero last week after being killed...