They just know that Najib is and are taking advantage of that fact. No surprise there. After all China is a country notorious for massive corruption. It always has been since the time of the Emperors and nothing has changed in that respect since.
So seeing an opportunity to fleece a crook vastly less clever than themselves they have grabbed it. One thing, and only one thing, stands between modern China and its imperialist ambitions and that is the US Navy. Despite all their efforts to match it they cannot and so must leave Taiwan alone and look elsewhere to feed their expansionist ambitions. The totally illegal land grabs of islands and reefs in the S. China Sea is one outlet for their imperial ambitions but there again the US Fleet stands in their way.
So when direct attack is not possible a way round is sought and one such presents itself in the shape of mega crook Najib Razak and his hangers on: notably fellow crook and fixer Jho Low. For what is to Beijing a derisory little bribe they gain control of strategically important Malaysia and become in positon to isolate Singapore and the shipping routes to the East.
Add to that Malaysia’s oil reserves, available more cheaply than Gulf oil, and the bribing of Najib makes good Chinese sense. It also weakens the position of the US in the Pacific and it will not be long before Malaysia is detached from Obama’s pet project the TPP.
Clearly nothing will come out of Washington before the result of the US election is known but whoever wins that will find a seriously weakened US position in the Far East and the Pacific areas. It will all be something that need never have happened if golf and personal pride had not led to deliberately closed eyes in DC. Let us hope that the new President is smarter. That would not be difficult.