Towards the end of that mission, go to the end of the train and go inside through the front and you,ll see the bomb. Crouch down and move that way, all the way till you get to the bomb, strait ahead, and stay crouched. And press (A) and hold it till it disarms.

I can't seem to get into the train. Once I get both hostages and the countdown begins, I get to the train and I can't seem to get into the thing. Help??
THanks

After you rescue the second hostage go down those stairs to the train platform. Once on the platform head right to the end of the platform and go down those stairs. Turn left and go strait through the opening in the wall at the bottom of the stairs and then go left again, up these metal stairs that lead to the back of the train car. Head through the train crouched until you get to the end then get the bomb. Mission Complete.

Hope that helped. My vocabulary is better usually but its late so I'm sleepy.