Drug runners? Perish the thought!
Back in the day, I worked for a major aircraft manufacturer. One of the old guard told tales of a long-ago new model airplane introduction...
The airplane, as is true of all new models, had some teathing problems - so many that the local rep would meet each flight along with the ground crew at the gate, go to the cockpit (no TSA then), and debrief the pilots before they left the aircraft. The rep would then head back to his office and transmit the info from the pilots to the engineers at HQ.
On more than one occasion, a flight from Europe would land at a major US east coast airport and the local rep would meet & debrief the crew in the cockpit, as usual. The captain would point to a wrapped package, about the size and shape of a framed picture, stowed behind a seat in the cockpit and say "That's from your friend." The local rep would finish the debrief, pick up the package and depart the airplane via the ground stairs, also as usual.
The pilots, in the mean time, would pack their things and head off the airplane toward Customs & Immigration along with the passengers.
Declaration? What declaration?