I suggest you google the phrase 'civil law country' or 'English common law' as I can't do the topic justice here.

The English legal system/philosophy (including jury trial and the adversarial prosecution/defense dichotomy) derives historically from English/Anglo-Saxon traditions (the 'common' law of England) and differs substantially in some respects from the legal systems in other countries which derive from Roman and later French/Napoleonic conventions (known confusingly as 'civil' law).

EDIT: although you mention civil law in your other comment - what I am getting at is the difference in role of judge/prosecutor in criminal cases between the two systems being comparable to GGP's suggestion