Headscratchers / Rush Hour

What exactly happened between Ricky Tan and Lee prior to the films?

So according to Lee, long ago, Ricky Tan and his father were partners on the force. Then Lee’s father found out that Ricky was working with the Triads. Before he could spill the beans, he was mysteriously killed, and after Ricky promptly resigned, the case was, for a while, dropped. My question is why did nobody, least of all Lee find this suspicious? Ricky should’ve been arrested long before Rush Hour 2, no?

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