The wiki on this heist says the following:
After gathering evidence, which is in the blue boxes marked "Clown Case", each box must be scanned (30 seconds each) until the traitor's DNA can be found.
Is this part a just a random roll if we picked up the correct box (trial and error) or is there a method to determine which DNA box is the correct one prior to putting it in the scanner? I want to cut down the overall time in the heist when attempting this on the Death Wish difficulty.
Best Answer
Not much seems to be available about this topic, but one short Reddit says that they don't know of any way besides trial and error. The same goes for the room where you search the bookshelves for the correct files. From my experience, it is completely random. There doesn't appear to be any clues given in the level or the day before hand that'll help you out for selecting the right box (given the nature of this heist, Day 1 shouldn't have any clues anyway).