Why no tracking dogs?

One of the police brass at last night's briefing said they had found blood a few blocks from the shoot out early Friday morning.. It would have been an easy matter to have had a tracking dog follow the scent from that point, and would have saved. Lot of effort and time. The same thing happened in the Chandra Levy case. Hundreds of officers looked and missed her body, but a search and rescue/cadaver dog would have found her in time to get forensic evidence.

I'm not trying to second guess here: I just don't understand why dogs aren't used more. Obviously they can't follow a suspect in a car, but they certainly could follow a bleeding suspect on foot.