there's a bit about wearing a hi vis vest, generally professional attire, a hardhat and carrying a clipboard will let someone maneuver around restricted access places unchallenged.
i assumed they found all this crap in his car, not equipped all at once. though that would be much cooler to see.
EDIT:
i looked up his arrest photo. his shirt is like something i would expect on someone who sells apple butter at a farmers market to be wearing to a pottery class at the annex.
The police and high vis vests are likely to blend in, either pre or post attack. The Nova Scotia killer wore a police uniform and drove a police car and pulled people over before shooting them