I say:
1) He knew Steve’s political views
2) Of course he knew about the purchases but
3) In light of (1) he probably knew something was coming ... soon
4) But Steve provided cash from whatever his source was (maybe he hit the lottery?) so he didn’t want to turn in the Golden Goose brother.
and somewhat to go down the old tinfoil road
5) He knew of brother Steve’s admiration of Antifa and/or ISIS. This one I’ll hold in the tinfoil category for now.
I suspect if old Steve would have been an extreme white nationalist that would have been our 2 seconds after the terrorist attack. Which makes me think he was left-aligned. Of course, I’ll also have to admit that’s tinfoil. At this point.
would have been OUT 2 seconds after
I think if Steve was a white nationalist he would not have shot up a country music concert. He’s a hard lefty that MAY have Islamo ties as well.
Even the baseball diamond shooter wasn't explicitly a member or supporter of antifa, so far as I know. The group isn't as big a thing in the outside world as it is for people here. It's possible that the Vegas shooter was a Trump hater, but he wouldn't have to be antifa or an antifa sympathizer to be that.
FWIW, you probably do find more supporters of Trump among country music fans, but in the blue states, you'll find a lot of country music fans who aren't fans of Trump. It's not 1970 anymore, and a lot of country music is basically pop. If he really wanted to strike at Republicans or Christians or Trump supporters leaving Vegas would have been a logical step.