Splinter Cell makes me angry

I've been playing Splinter Cell: Pandora Tomorrow off and on for a while now. I know, I'm behind the times, but I'd really like to finish this one before I start on Chaos Theory.

Anyway, I'm on the mission inside LAX, and I'm right at the end of it. I have to kill 3 terrorists in the catwalks of the airport, and then pick up the sample of whatever the virus name is. Shouldn't be too hard, but once the terrorists know I'm there, I have a minute to kill them and get the virus. Slightly harder.

There are also 3 civilians walking around, and I can't kill them, obviously. However, if they say anything it tips off the terrorists, and they promptly kill me until I die from it.

I have a system of shooting out lights and knocking out civilians, and if I can avoid catching attention until I get up near the terrorists, good. Otherwise I die. As soon as I get near them, however, I can't kill them. Either one of them manages to shoot me from across the room (in the dark, without having anything to mark my position), or I can't see the one who's shooting me, or any possibility of it going all wrong.

I've tried every possible vantage point. I've shot them from below, I've shot them from above, I've shot them from the same level, and I can never get them. Once, and only once, I managed to kill them all but then couldn't get to the virus before time ran out. If I was an angrier person I would have thrown the controller through the TV.