A clever robber breaks into a closed bank where he finds a clerk. He asks password of the safe from the clerk while pointing a gun on his forehead. Out of fear, the clerk manages to blurt out, “Every day, the password of the safe is changed. I can help you but please point away the gun as if you kill me, you will never be able to crack the password.
The robber ties the clerk on a chair and insert a cloth in his mouth. He then easily opens the safe after inserting the code and takes all the money before he flees.
How did he know the password ?