Complex sentence: In 1985, key expert testimony against Zündel's alleged Holocaust denial was provided at great lengths by Holocaust historian Raul Hilberg, who refused to testify at Zündel's 1988 trial.
Split into simpler sentences: In 1985, key expert testimony against Zündel's alleged Holocaust denial was provided at great lengths by Holocaust historian Raul Hilberg. Hilberg refused to testify at Zündel's 1988 trial.