Hi xkatelpx,
This game is very picky about evidence being examined thoroughly. To be absolutely sure, re-examine Ratchett's hat in your inventory and see the Rev. 13:18. Then check the documents in the scrapbook for the bible passage which mentions 666. Those are the triggers you need. Now try the safe again:
Turn by placing the cursor on the left of the dial of the safe (counterclockwise) and click to get 6 under the line.
Place cursor on the right (clockwise) and click to get 6 under the line.
Place the cursor on the left of the dial of the safe (counterclockwise) and click to get 6 under the line.
The safe is opened. 'I think I heard a click.' Turn the handle.

and let us know how you get on.