SAN ANTONIO (AP) — An American tourist was shot in the back of the head in Mexican waters on Thursday after being ambushed by armed boaters, a Texas sheriff said. It happened near the U.S. boundary of a lake where run-ins with pirates already had fishermen and Texas officials on alert. Zapata County Sheriff Sigifredo Gonzalez identified the victim as David Michael Hartley, 30. Hartley and his wife were riding personal watercrafts back from Mexico on Falcon Lake when about six gunmen approached in two boats, Gonzalez said. The sheriff said Hartley was shot as the couple sped away at...