Its extremely easy to detect if collusion is happening or not. Its called common sense. if you see the same 3 players all playing together at multiple tables at a time, THEY ARE COLLUDING!
ITS NOT A MATTER OF OPINION.
Frankly I hope he serves time for theft and fraud.
What if you're only 99% sure they are colluding? If you have a big penalty, then you couldn't afford to have false-positive's of 1 in 100. If the penalty is light, then people can afford to keep trying.