Originally Posted by autdi

If all pre-clearance is like YYZ, then you go through the passport check and the customs bag check, with the forms all done before getting to security, and there was a bag drop post customs, but before security for checked bags. Think of it this way, if you had something in a carry on, you exit into the secure side of the airport on arrival, not the sterile path to customs, so anything customs wanted to look at had to be done before you leave, as you are treated like a regular transfer on arrival in the US.