Aim where I aim for the first rocket shot. You want the rocket to make it to that back corner/where the two walls meet, and then explode. If you aim where I aim for the second rocket shot, there's a chance it kills him, but there's no guarantee. The rocket will sometimes explode to the left of the 'Injury Care Unit' sign, rather than make it to the back wall and explode where the two walls meet.

How do you know you've pulled off the shot? Listen/watch (subtitles) for Anthony's dialogue, "Argh... my arm... Peg... Peg...", followed by Niko's, "No one likes a rat."

Additional video(s):