All right, long time lurker but decided to join when I saw this information:
"It’s possible that Taylor knew of the Girl Scouts camp because he went in the area to test HAM radios that he built, Alberti said"
I am an Amateur Radio Operator myself, it his not uncommun to go were there is no interference from power lines, LED, cheap chineses devices etc to play with our radios,
but also, to become a ham radio operator, you need to pass a test to get your licence.
Now you can be tested by volunteers but at the time, you needed to pass your examination at an FCC office.
I ham not sure of what the rules were in the US at the time (I'm Canadian BTW) but I think when you got your ham certificate at the time (they are several levels), you also needed an radio station certificate for your radio station in your home, I don't remember if you have to renew your certificates every year or every 5 year but now, the radio station certificates dosen't exist anymore and your Amateur Operator Certificate must be renew every 10 years (in Canada it's valid for life now)
At the time, before the internet, every year there was a directory published for ham operators displaying names, callsigns you have and your adress, exactly like a telephone directory, it was called: Amateur Radio Callbook.
For most of us, we have studied hard to get that certificate so we usually renew it all our live, anyhow the Callbooks are all on the web if people want to do some sleuthing:
Summer_1963_Radio_Amateur_Callbook : Free Download, Borrow, and Streaming : Internet Archive
Colorado is in Call area 0 (zero)
Link for Callbooks from others years:
Amateur Radio Call Books : Free Texts : Free Download, Borrow and Streaming : Internet Archive
Nick - Amateur Radio Callsign VE2NCG