Most JAG offices retain several highly trained investigators to inquire into wrongdoing, or possible wrongdoing. Typically, these investigators travel with their own security teams, and standard protocol calls for a starship captain (or starbase commander) to put the ship’s (or base’s) security forces at a visiting investigator’s disposal. Their task is to gather facts and evidence and determine if a Courts-Martial is warranted. JAG investigations continue until the case is solved, or no clear determination can be made (at which point the file is left open until new evidence may be brought to light.)
When the death of a Starfleet Officer happens, the Judge Advocate General will authorize the Starfleet Criminal Investigative Service (S.C.I.S.) to look in to the death.
Although all Starfleet captains can call for a JAG investigation of personnel under their command, most ranking officers prefer to conduct their own inquiries and submit their own subordinates for courts-martial. Normally, JAG investigators become involved in a case only when a member of Starfleet is accused of wrongdoing by someone outside of his chain of command. If no JAG officer is available to conduct an investigation, it falls to the highest ranking officer to appoint an investigator -- normally the ship’s Security Chief. Starfleet personnel who show particular aptitude in law, or who attended law school on their homeworlds, are frequently tapped to serve in the JAG Corps for at least one tour of duty. This is not restricted to those with a legal bent, however, the JAG office requires officers with a nose for the truth and an unswerving devotion to the principles, rules, and regulations that govern Starfleet. Security officers, science officers, or other experts in the field could find themselves detailed to the JAG Corps for a particular investigation. The Centre for Advanced Training provides classes to those who desire legal training, most notably those Command personnel aiming for promotions to Starfleet’s upper echelons.