All articles I read about this said that Ma's only involvement was that the prosecutor presented a report to Ma of information they gathered before the probe was completed. In all of the articles I've read about the Wang case, I see virtually nothing implying that Ma himself was involved in the wiretapping or even the instigation of the investigation. What was his crime? What evidence is there that he committed such crime?
This article (from the heavily green-leaning Taipei Times) gives the same summary that I've read over and over: taipeitimes.com/News/taiwan/ ... 2003578065
So the prosecutor's office was running an ongoing investigation on Ker, overheard a conversation in which Wang was engaging in questionable behavior, and then reported it to Ma. How is Ma guilty of any crime in that series of events?
Now Ma then went on to use that questionably-obtained information in a questionable manner. He used it to try to push Wang out. Since the information was gained through improper means, it wasn't proper to make it public and try to leverage it into a way to push Wang out of the party, but as far as I know, those actions while perhaps morally lacking, aren't ILLEGAL. This is an example of Ma being a poor politician, not a criminal.