To be honest, it is more likely that the prosecutor is the one who has ulterior motives, such as trying to get revenge on behalf of one of the prosecutor's friends/family. Or even just for personal career advancement.
I could see equally likely, but more? Why more?
We recently saw a corruption scandal, which went through to indictment, against another Korean family [1]. Park, to whom Lee has been connected, has already been impeached [2]. The preponderance of evidence I've seen favours the prosecution.
[1] https://mobile.nytimes.com/2016/10/20/business/international...
[2] https://www.bloomberg.com/news/articles/2016-12-09/korea-s-p...