A very good friend Reb J.R. sent me a booklet written about the Gaon Rav Avraham Genechovski ztz"l Rosh Yeshivas Chebin, and there are some PHENOMENAL stories there. Here is one [and more to come bl"n].
The Chebiner Rov, Rav Dov Berish Veidenfeld [d. 1966] NEVER got angry [even though he had many reason to] except for ONE TIME. There was a certain Nazi on trial in Israel for war crimes. A Jewish man was hired to testify on this Nazi's behalf [what a Yid won't do for a little parnassa..]. The Chebiner Rov asked to call the man in to see him because he knew that this Nazi was very guilty.
When the "witness" came in to see him the Rov started shaking him 'like a lulav' and said "If you testify, I will uproot you from this world and from the next world."
He listened and refrained from testifying on this Nazi's behalf.
Rav Genechovski discussed the halacha in this instance. Must he return the money that he was paid for the testimony? He proved that he doesn't from the gemara in Rosh Hashana that says that false witnesses who were hired to testify about kiddush hachodesh need not return the money.