At present, all cases in Japan are tried by judges. The percentage of people tried who are found guilty is in the high 90s, so a lot of innocent people must be going to prison. An article on Japan Today, a useful news site, says:
The law stipulates six people will be selected per case to work with three professional judges at a district court in court hearings. They are expected to decide a verdict and sentence by a majority vote.
I think random selction is an excellent way of guaranteeing representativeness, not just for trials, but for legislative bodies too, although that's been out of fashion for quite a while.