It's not really a theory, fairly certain the AFL tipped them off - IIRC Hird stated this under oath in court.
The AFL did not however hang them out to dry they carefully managed the process so the AFL tribunal cleared everyone - only because WADA appealled did the whole charade come crashing down.
Correct. The AFL and Essendon had it all worked out until WADA became involved. That is abundantly clear.