Play the secret first person battle mode
To unlock the first person mode all you have to do is simply complete the game.
Submitted by Paul_Smith. 100% success rate. 

DIJ's Diary Location
DIJ's diary is in the slot machine in battle mode. You may have to play more than once to find it.
Submitted by ChuckRock77. 

Infinite Ammunition
Enter the item selection screen, then press Up, Up, Down, Down, Left, Right, Left, Right, R.
Submitted by Paul_Smith. 0% success rate. 

Rocket Launcher
Get an 'A' ranking in the normal game by completing it without saving, no first aid sprays, and no retries. Additionally, save Steve from the Luger quickly, give the Medicine to Rodrigo, and complete the game with a time less than 4:30. The rocket launcher will appear in the first item box in the next new game.
Submitted by Johnny_Wilson. 

Solution to the seven paintings puzzle
About five hours in on the first disc you'll find a room with seven paintings, each with a switch below it. In order to solve the puzzle you must press the switches below each painting in the correct order. Below is the order in which this must be done:

1. Painting of the woman.
2. Man with two babies.
3. Man by himself.
4. Man with plate.
5. Man with book.
6. Man with candle.
7. Big painting.

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