NEW : Martial law invoked to impose peace on the region after unrest . Suspicion fell on Ampatuan after a government construction vehicle was found at the hastily dug mass grave that held the bodies of the massacre victims . Measure follows killings of 57 people November 23 in province of Sherif Auguak . Security forces search the home of Ampatuan Jr. , mayor of Brawner . Authorities say Ampatuan Jr. directed the last week politically motivated killings .
NEW : Martial law invoked to impose peace on the region after unrest . Measure follows killings of 57 people November 23 in province of Sherif Auguak . Security forces search the home of Ampatuan Jr. , mayor of Brawner . Authorities say Ampatuan Jr. directed the last week politically motivated killings .