In the final duel with Maddox, kill him with the first shot ("No Loose Ends")

Complete the game on Casual

Complete the game on Expert

Collect all secrets in Act 3

Complete Act 2

Kill Major Vladic ("And Justice For All")

Achieve 100% accuracy in any single player mission

Collect all secrets in Act 1

Take 50 headshots in single player

Rescue the friendly ("From Out Of Nowhere")

Take a successful shot from a distance of 1 km or greater

Kill 50 enemies while holding your breath

Finish the 'The last hunt' mission.