I have been wondering about the spy in a bag with the locked zip.
Putting the padlock on to the two zip fasteners after closing the zips might be difficult from the inside.
However it appears from the pictures I have seen that the two zip fasteners would move along the zip when locked together.
So could the spy have put the lock on the zips whilst outside the bag, forced the zip open between a zip fastener and the end, climbed in the back and then perhaps with some difficult slid the fasteners along the zip to close it, and then back to the middle position?
It might not be easy but the spy was a slender keen cyclist, so possibly quite strong.