Half way through the game after speaking with Talya in her office, Paul will randomly send you a message, it's not really Paul. At that point go to the security office and speak with the other guy in there and ask about Paul, find Paul further down the corridor and talk to him. From this point a cutscene will happen and take you to the lab along with security, and after Michio traps you security will arrest him.
You can use my video below to guide you on this if needed: