There's no catch all 5e style investigation skill. You should be able to use a number of different skills to investigate with though. Perception to go over a crime seen looking for clues. One of the sciences, culture, engineering, medicine or mysticism to get information about said clues. Bluff, intimidate and diplomacy could all be used to question witnesses, with sense motive to try and ascertain any lying or duplicity. Survival to track down a someone fleeing the seen. Disguise or stealth to help stake out a location. Computers to break into a terminal to gain pertinent files. Only skill I don't see being used are piloting, sleight of hand and athletics/acrobatics. Though you could probably get inventive with those even.