I couldn't get that link on my iphone so I looked up the shooting and found this:

http://m.youtube.com/watch?v=12t3u9sWhK4

The witness in the video seemed a little dismayed by the lack of assessment by police before rushing in to use lethal force. Obviously, this individual could have been tazed, disarmed and taken into custody without too much difficulty. There was really no need to open fire like that. But you have to understand, to them he was not quite human, they didn't value his life. He's was a problem. Problem solved. It's getting more like that in case you haven't noticed. Makes you worry about ever winding up in the wrong place at the wrong time. Mistaken identity could get you killed.

Police now fear any kind of physical contact whatsoever. They consider it an imminent threat to their personal safety. It doesn't even have to be violent contact. They fear anyone who is not 100% obedient to their commands. There are no extenuating circumstances in this regard- no allowances made for mental illness, injury, intoxication or substance abuse, dementia, whatever- zero tolerance. The link below illustrates this point.

http://portland.indymedia.org/en/2006/11/348748.shtml

To answer your question, they protect and serve the state. They're part of the state apparatus. They answer only to those higher up on the food chain, not to the public who foot their paychecks and pensions and most certainly not any member of any disenfranchised group.