In this recent NJ criminal appeal, the Appellate Division reversed the defendant's conviction after finding that the trial judge improperly questioned the defendant's witnesses. This gave the jury the impression that the judge doubted the witnesses' credibility.
State v. Peter J. O'Brien, ? N.J. ?, 2009 N.J. LEXIS ? (December 29, 2009) - Conviction reversed because the trial court's questioning of defendant and other witnesses ran afoul of State v. Taffaro, 195 N.J. 442, 451 (2008). "At trial, defendant did not contest the fact he killed his parents; his sole defense was diminished capacity, which was to be proved through his testimony about his drug consumption and depression, and that of his expert psychiatrist. During the trial, the trial judge injected himself into the case by questioning witnesses, including defendant and his expert. Because that questioning made it seem as though the judge did not credit the proffered defense, it denied defendant a fair trial.... [A] judge has a right to question witnesses in a criminal trial. But that right is tethered to ensuring the fairness of the proceedings, to expedition, and to the clarification of ambiguities. None of those matters was at issue here. Here, the judge's questioning was gratuitous and evidenced incredulity with respect to defendant's only defense, along with support for the State's witness. As in [State v. Guido, 40 N.J. 191, 208 (1963)], the 'judge's repeated assurances to the jury that he was acting in the interest of justice with no purpose of aiding or hurting the prosecution or the defense' rang hollow and were not sufficient to cure the harm...." See also JURY INSTRUCTIONS. (Jay L. Wilensky, A.D.P.D.)
http://www.judiciary.state.nj.us/opinions/supreme/A-89-08.pdf
