@ZG47 that one persons complaints about the gun club need to be taken with a grain of salt. A member of the gun club I personally know has stated he met the "shooter" at the gun club about one month ago. He seemed perfectly normal and nothing in his actions, demenor, words, or dress indicated anything unusal.
The person in the video making the complaints also claimed to have met the "shooter" at the club on the visit in question. This was in Nov 2017, but the "shooter" didn't join until early 2018.
From everything that has come out about the shooter there is nothing to indicate that he had any mental health issues or was in anyway an "abnormal guy", apart from his strong anti-muslim ideology. Going by this it is not difficult to believe that he would have probably kept quiet about his beliefs in front of people he did not know. He also appears to have self radicalized using the internet or the dark web in particular which would have allowed him a greater deal of anonymity.
As an interesting aside this article compares the firing rates between WWII and the Vietnam War (when specific indoctrination was actually used to dehumanize the enemy and focus on killing the enemy) https://greatergood.berkeley.edu/article/item/hope_on_the_battlefield The study found that in WWII when no specific training about killing and dehumanizing the enemy was used firing rates for soldiers were at 15-20%. In Vietnam when they actually introduced training for it the firing rate went up above 95%. But I think they found that across the board 1-2% of humans are natural born killers- they have no problems killing another person even with no specific training for it. A small majority but it does add up when you consider the world has billions of people. Did this guy self indoctrinate to view Muslims as sub-human or was he one of the natural born killers I don't know...