That does sound like someone who lost control of an aircraft to me. I'm not a pilot, but if you know you were about to slam into a building, would you go full throttle on your engine?
IMHO...IF you were purposely aiming at the building...you would to try and maximize the damage.
NTSB spokesman is saying this was an intentional crash.
Breaking on Fox...the pilot set his house on fire before going to his plane and flying it into the building that houses the IRS.
NTSB is treating this like an intentional act.