Judge Sahara Silongan, who had served as Cotabato City administrator in the late 1990s, was driving his car home from the citys downtown area when the suspects overtook his vehicle, blocked his path and opened fire with .45 automatic pistols, killing him on the spot.
Silongan was a former member of Maguindanaos provincial board.
Witnesses told investigators the motorcycle-riding gunmen casually left the area after shooting Silongan.
The police still have no solid clues on the identities of the suspects or the motive behind Silongans murder.
There has been a rash of brutal killings here of ranking government officials since January, in seemingly unabated attacks that have spurred criticism of the city police.
One of the people recently killed by suspected hired assassins is lawyer Arnel Datukun, who was manager of the World Bank-assisted Autonomous Region in Muslim Mindanao (ARMM) Social Fund Project at the time of his death.