Philippine officials have arrested a powerful official in Maguindanao and imposed martial law in the province after the massacre of 57 people there. Official sources said Andal Ampatuan Senior was arrested at dawn along with another senior member of the powerful clan. Andal Ampatuan Senior's son, Andal Ampatuan Junior, turned himself in last week and was charged with 25 counts of murder. The move comes after troops raided compounds belonging to the family and found an arsenal of buried weapons. <br/>Prosecutors have issued subpoenas to six members of the Ampatuan family including Andal Ampatuan Senior to appear at a hearing on 18 of this month. <br/>Among the 57 victims were members of a rival clan and 30 journalists.