Yes, I would have had K9 involved immediately. At this point, I have no reason to believe that K9 was not involved, I just haven't seen any footage of any tracking happening. It could have happened though, I don't know.
One problem is that for K9 to effectively track, you can't have 9,000 people running all over the place. It messes up the track and is distracting to the animal. Normally you set up a perimeter, and K9 searches inside that perimeter with all other officers staying back / behind K9.
http://www.globalanimal.org/2013/04/19/will-dogs-nose-for-crime-find-second-boston-bomber/95856/
There were dogs used in the search and you are probably correct that 9000 people messes up the track. I was told that initially the dogs traced the suspect to basement of house. The suspect was hiding there but had left. The dogs could not find the suspect after this location.