Generally, yes, I trust police officers. I've never experienced any kind of bad behavior by a police officer, in fact, I've experienced pretty cool behavior (like letting me out of a speeding ticket because I had just moved from Arizona to California).
But you can't ignore the problems in other parts of the country. And that while someone may be a good, hell, a GREAT cop, when it comes to opinions on one of their own that might be a bad apple, they might stay silent to protect him, however bad that other cop might have behaved. It's a fine line.