The Gates 911 Call
I've listened to the Henry Louis Gates 911 call, and it does not look particularly good for Sgt. Crowley. The woman who called doesn't really have any opinion on whether a burglary took place or not, she raises the possibility of the people living there, she notes the presence of suitcases, and she really only made the call because an acquaintance asked her to do so.
The dispatcher relays most of the information to Sgt. Crowley, and Crowley apparently didn't check with the 911 caller at all:
“She didn’t speak to Sergeant Crowley at the scene except to say, ‘I’m the one who called,’ ” said the lawyer, Wendy J. Murphy. “And he said, 'Wait right there,' and walked into the house. She never used the word black and never said the word backpacks to anyone.” [...]
After Sergeant Crowley arrived at the home, according to the tape, he radioed that he was with a man who “says he resides here,” but he described him as “uncooperative” and asked for backup, saying, “Keep the cars coming.” He also asked the dispatcher to “send the Harvard University police this way.”
You can read plenty of your own biases into this, but stripping it down to the bare facts, you have a 911 call saying that two men maybe broke into a house but they could live there, the cop arrives and confirms that the man lives there, but then he calls him "uncooperative," brings out other cops, and arrests him.
This question divides a lot of people, but the moment that Crowley confirms that Gates is in his own home, he has no reason to be there.
Anyway, I'm sure it'll all be settled by beers at the White House, anyway.