In the 5th episode, part 2, Blood Money there is a safe containing a hidden evidence. The safe is behind a coded door (4-1-5 is the code) and up a staircase next to a painting. If you go into the security room where Victor Yavlinsky is, you will find a pile of money with a calulator next to it. The green calculator screen will have the numbers "91.9" on it. If you run up to the safe and enter in the digits 9-1-9 the safe door will swing open and the hidden evidence will be all yours.
In the bonus level "Goodnight Sweetheart" you play as Stone and have to kill Elsa. There are three guards watching out for intruders. If you kill all three of them without being seen you will go into a special cutscene. You will see Elsa and a female scientist that came into Elsa's house at the begging of the level, outside on the balcony with little clothes on kissing. You must also have the difficulty on hard to see this easter egg.
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