When you break into the science lab, do not take the lab coat. Instead, continue on with all of your weapons and try to keep the alarms from going off -- nothing happens if it does. When you hear about the door with the security code, find a guy man who sits at a table and does not do anything. There will be a red set of brackets around something that does not exit. This is where you get the key to the locked door, by killing the man who does not talk. A key card will appear where the set of red brackets where located, and you can continue.
