Kootenai County Sheriff Bob Norris told a news conference on Monday that Roley had once aspired to be a fireman.
The suspect's grandfather also told
NBC News his grandson had "actually really respected law enforcement".
Dale Roley said his grandson "had been in contact to get a job with a fire department", and "wanted to be part of a team that he sort of idolised".
"He loved firefighters," said Mr Roley. "It didn't make sense that he was shooting firefighters. Maybe he got rejected or something."
Sheriff Norris said the homeless suspect had attacked fire crews after they asked him to move his vehicle, which he had been living in.