Seems like the guy is "disappointed" with someone else, specifically the public safety. So, he judged them by interfering with them. If you don't like hearing what they're doing, just turn off your radio!
Chain of events:
May 31, 2018 - initial complaint. Interviews of possible suspects start taking place.
[2 months]
July 24, 2018 - Letter of Inquiry to trombone player.
August 20, 2018 - Complainant reports cessation of interference
October 3, 2018 - Response to Letter of Inquiry
October 17, 2018 - Resumption of interference
[5 months]
March 29, 2019 - FCC brought agents to do RDF. They actually had agents do covert monitoring - they followed the trombone player around and caught him in act. He was playing back the sad trombone sound into the microphone of a radio in a car... how much more primitive could that be...
[ 2 weeks]
April 10, 2019 - FCC had agents to do RDF again and found/followed trombone player around again and caught him in act again.
June 18, 2019 - This letter.
Seems like they had a suspect within 2 months not due to RDF but to interviews. I wonder how long it would take to find the interferer if there were no suspects and it were some random unrelated person. So far all these interference cases tended to be a grudge holder that people knew.
And then if it were on part 95/97 frequencies. Perhaps it's not because of 95/97 that cases are not solved, the only reason why this (and any other) one got solved is because they had a suspect early on.