Searchers make arrests , recover arms from a clan implicated in massacre . Martial law follows killings of a dozen last week in the Autonomous Region . Several members of powerful Philippine political family detained . Andal Ampatuan Jr. Mayor Datu Unsay directed killings , authorities say .
Searchers make arrests , recover arms from a clan implicated in massacre . Martial law follows killings of 57 last week in Maguindanao province . Several members of powerful Ampatuan political family detained . Datu Unsay Mayor Andal Ampatuan Jr. directed killings , authorities say .