It was already long-standing practice, when I was teaching many many years ago, to interview suspected cheaters (it's usually quite obvious) to see if they actually knew what they claimed they knew.

Only the dumb ones are obvious. In my school (SFU/BC) most of the students in almost all of my classes cheated. VERY FEW got caught.

I heard instructors say all too often that it was obvious when somebody was cheating, but somehow they missed the guy paying his cousin to write the final.