Now we need to break into the FBI themselves to steal info we need. Seems like a mission that you should stealth, but you really don't need to.
Charge into the building and search the place for this security door. It's alarmed, so if you haven't sounded the alarm, this will seal it. Pretty weak for the FBI, just pick it open.
Enter the small room to find a heavy security door, this is slightly more like it. Drill it, C4 it, ECM it or Saw it.
Since we blew stealth, a grate came down that we need to drill through. Hold on either corner on this drill, the glass is Bulletproof and the door provides the perfect choke point for holding out. Grab the server once the drill is done.
If you're disappointed by the lack of loot in this day, look for a wooden door and open it. There is a sealed off area that sometimes has some worthwhile loot in it.
The only thing you need though is the server, so throw that into your truck and get outta there.