Originally Posted by wjustin
the big blind does not respond.
This is going to be the problem - if the big blind made no response, then it can't be proved that any collusion took place. The big blind has actually done the right thing in not responding, by the way.
If the big blind said "OK, we'll check it down" then it would clearly have been collusion. The action that could have been taken would have depended on the rules of the casino (assuming this is live).
In any event, if this is live you need to speak to either the dealer or the floor manager / tournament director at the time
and ask for a ruling. Online, the site administrators can go back and look at chat logs etc., but live if the floor isn't called over at the time, there's not much they can do.