When the final boss walks towards Anna, light up his back either with the AK47 or MP5, each one has the rate of fire you will need to get his attention. Then as he rushes you, run at a angle away from him then go perpendicular from the boss' path at the last second.

Repeat at least four times while Anna sets those charges! After a cut scene, you must switch to the .45 pistol to finish him. You use the same dodging strategy as before but this time, you have Tom run towards the boss' left side (that will be Tom's right side) and the boss will usually miss the claw attack and instead pick up your character to crush him.

Strangely, this is what you need to do. Only up close can you press the ACTION key (RED on XBOX) repeatedly to fill the action gauge to full and then press FIRE (R on XBOX) to shoot the boss at point blank range. Do this 3 times and you're done!