Indeed, the corruption in the Philippines notwithstanding, they do not mess around with this sort of criminals.
Unfortunately, they (Philippine gov't) cave in to these criminals (actually, they are far more than criminals) regularly.
This Mayor Ampatuan is evidently part of the same clan ("warlords", says my Filipina wife) whose forces killed a large group of local journalists and other civilians on 11/23/09. If anyone is not familiar with this horrific crime, you should be:
http://en.wikipedia.org/wiki/Maguindanao_massacre
Note the lack of justice...
That said, the Ampatuan clan probably did not attack the police in this case - at least not directly. In this latest incident, and drawing from the Fox / AP article, it is notable that the target of the police raid is one Zulkifli bin Hir, a Malaysian terrorist who's been hiding in the Muslim part of Mindano for over a decade. The Moro Islamic Liberation Front is strong in the area (as in so many parts of the Muslim world, there are various factions who may or may not cooperate with each other, any given minute.) It's a pretty safe bet the Moro's (or friends) have been shielding bin Hir. I would not even be surprised to learn that this was a flat out ambush with the Philippine police carefully "set up".
It's also interesting that "foreign truce monitors intervened". Too bad it wasn't a couple of U.S. helicopter gunships or A-10's.