It wasn't a left-wing group, but it appears to be a lone wolf that has views more aligned with the left than the right who didn't like a guy with views more aligned to the right.Of course they aren't going to. It's not like people on the fringes of society have membership groups. Statements like "well the shooter was a card carrying KKK member" or "he was a known member of Antifa". No. There is no group called "The KKK" or "Antifa". No membership cards or rosters. Both these "groups" are just people that consider themselves members of what they think that group should be and they chat on the dark corners of the internet.
I personally never thought Kirk's shooter was a member of Antifa, or one of any other leftist leaning "community". He was just a crazy, misguided person that shared beliefs on issues that matched the beliefs on the left side of the aisle. I guess that makes you a leftist. I don't know. I don't think it makes you a leftist any more than voting for a Republican makes you right-wing.
What this was not - as far as we can tell right now - was a guy who thought Kirk was too moderate.