I have experienced this situation a couple of times when a candidate is giving an interview in front a panel (in some cases, they are senior but not boss, and other times, they are colleagues of same rank), and someone from the panel goes hard at the poor candidate (which is a nervous creature to me for most of the cases) and shakes his/her confidence a great deal. They ask some unnecessary/too difficult questions in a technical interview, when the candidate needs some basic questions to let him calm down and feel at ease.
I (and some of the other co-interviewers) have often found it pretty up-setting as it ruins the whole purpose of an interview. Once I tried to interject during an interview to calm things down, but was immediately shushed and told "Don't say any such word in front of the candidate." The interviewer (being senior than me) agreed with me but asked me to shush as it would leave a bad impression in front of candidate. I did raise this issue in private with that interviewer later on and despite agreeing, I didn't see any change I am afraid (hence this question) .
How can I address the co-interviewer's attitude during the interview so that the candidate is treated more respectfully?