Upon breaching the fortified building, you'll engage in a fierce battle with the Spec Ops Commander's elite guard. This will be one of the toughest human-on-human encounters so far. The room will likely have multiple levels and cover points. Use grenades to clear out entrenched enemies and focus fire on the most dangerous threats. Once the elite guard is neutralized, the Commander will attempt to escape or make a final stand.
Subdue the Commander (usually by depleting their health and then interacting with them) to initiate an interrogation sequence. During the interrogation, you'll need to defend your position from waves of incoming infected and possibly more Spec Ops who are attempting to rescue their leader. Protect the operative performing the interrogation at all costs. The interrogation will reveal crucial information about the US government's plans and the location of a new threat.