Press Up, L, Down, R, Left, L, Right, R, Up at the mission selection screen in either single player or cooperative campaign mode to unlock all missions in that mode.
Compliance
In every level you are required to arrest a certain number of suspects. Instead of shouting, if you prefer the assault rifle just shoot the suspects four times then shout for compliance. Sometimes they will give up[ others may die. Test this strategy on different people and find which ones may die when you shoot them.
Get Inside Building
When playing in two player mode, at some point you will reach a mission where you start behind a big pile of sand. First, clear everyone on the other side of the sand pile. Then, go back to the sand pile. Get directly on top of it and you will see a ledge beside the pile. Walk on the ledge and keep going until you reach a new area. You are now inside, or close to the entrance of the door.
Invincibility
Press Start to pause game play, then press Up, Down, Left, Right, Left, Right, White, Black at the options screen.
Mission Ten
Mission 10 ( the last level) is just an outgoing mission. All you have to do is eliminate everyone or restrain a few people. Do not worry about stealth. Just take aim and run and shoot. You will not fight Carter and do not worry about trying to get better parts on your gun for the mission.
Unlimited ammunition
Press Start to pause game play, then press Left, Right, Up, Down, Up, Down, Black, White at the options screen.
View Game Developers
When playing in two player mode, go to the mission where you have to protect Furious Thug. At some point you will reach a room with a lot of chairs and a jury stand in the front. Look at the walls until you see some pictures. They appear to be the game developers.