My memory is not that good. Border stations will fly their flags at half mast if former presidents or members of congress die, or if an INS or Customs officer is killed in the line of duty. Also state governors can call for the lowering of flags.
This is a commonly photographed building because of the huge boundary marker right by the front door. I recall seeing a picture of it (and it's owner at the time) in the 1983 book about the US-Canada border "Lakes Peaks and Praries".