We have killed everyone in the train station. We have also already read all of the information on the computer. What should we do next and where should we go?

So it would seem you're playing co-op mode of Chaos Theory, correct me if I'm wrong.

What objectives are completed/not done in your OPSAT? Check the list below:

Objective: Figure out Kim’s objective
Objective: Bug telephone in main hall before Chu gets to it to listen in on Chu
Objective: Deactivate bombs (3)
Objective: Get antidote from locker
Objective: Eliminate contaminated soldier in bathroom

Opportunity Objective: Get schematics of bombs
Opportunity Objective: Follow Chu to the locker
Opportunity Objective: Secure toxin from the infected soldier.

NOTE:
If you've made it to the infected soldier, grabbed the vial and killed him, you need to look up above you in the bathroom for an opening. Do the boost/ladder maneuver and crawl through the vent to the next area. If you've already done that and are wandering around in the lower area, let me know and I'll spill the beans on what you've got to do next...