The thief would play their game and win.
Waiting for the meeting they were attending to take a break, the thief looked over his talking co-workers. Believing they would never figure out who was doing this, the thief feel safe.
When the meeting took the break, the thief snuck into the offices taking their pen, pencils and paperclips. These were placed on a desk before going back to the meeting smiling with success.
Later that evening at their supper table except Napoleon, the agents met and confirmed their office supplies were taken again.
"Let us catch a thief," Illya said.