§1. Each of the experts is to prepare a report separate from the others unless the judge decrees that one report signed by the experts individually be drawn up; if this is done, differences of opinion, if there are any, are to be noted carefully.
§2. Experts must indicate clearly by what documents or other suitable means they gained certainty of the identity of the persons, things, or places, by what manner and method they proceeded in fulfilling the function entrusted to them, and above all on which arguments they based their conclusions.
§3. The judge can summon the expert to supply explanations which later seem necessary.
Source: Code of Canon Law (Vatican.va)