To open a safe in the 5th episode, part 2, Blood Money, open a secret door (enter 4-1-5 as the code) and go up a staircase next to a painting. Find a pile of money with a calulator next to it in a security room. You will see the numbers "91.9" on its screen. Now go to the safe and enter in the code 9-1-9 to unlock the hidden evidence.