I've only played Blood Money since I am using a PS2 as of now Level 3 was very challenging but I got through it eventually. Keep trying All about strategy. Also some advice, try distracting them with an explosion somewhere else. Maybe a remotely triggered bomb or something. I don't know if it's possible with the equipment you have on that mission but that's what I would do if it was possible.
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That strategy actually helped me distract the guards in Mission 3 of Blood Money. They were distracted long enough to let me strangle the painter with my Fiber Wire and take his clothes then drag his body through a door. As a bonus it took out 1 of the 2 targets