...and precisely the reason that jury nullification is an issue in America. The judge becomes judge and jury when he shuts out certain testimony that IHHO is not relevant and requires the jury to bow to his views on what should and should not come into his or her courtroom.
Some might say that is the right of the judge, others, especially the accused and the jury, might not agree.
Judges are certainly very powerful, which is why it's so important to have competent, fair judges. In principle I like the idea that jurors shouldn't conduct their own investigation. There's simply way too much potential for abuse there. I admit that I didn't follow this trial very closely but it seems like the judge gave both sides ample opportunities to make their cases. If one side had a weak argument it's not the fault of the judge.