Out of Political Favour

The Rt. Hon. Yong Teck Lee is now being subject to an Anti-Corruption Agency's investigation over his RM5.0 millions deal during his tenure as the Chief Minister of Sabah. But what surprises me is the timing of such action following his statement on a potential withdrawal of the political party which he presides from the ruling National Front (BN) and his intention of pushing a Vote of No Confidence in the current sitting of the Parliament. Obviously this did not materialise when he, as the proponent of such motion, was absent from the parliamentary session.
The question is whether such action against him would have been triggered at all had he chose to remain a loyal member of the ruling coalition. Why now ? Wasn't the powers that be aware of such case as it happened then ? Was the 'malpractice' condoned by his political peers then when he was still a powerful BN supporter ?