I don't think it's all that much of a mystery - Trumpers are desperate to pin Kirk's shooting on a "radical leftist" who was either "indoctrinated" by radical college professors or was somehow connected to transgenders or another group they hate. That would give his shooting meaning to them, as it would confirm in their minds that Kirk was indeed a hero and Christian saint who died fighting for his (and their) beliefs at the hands of their mortal enemies, the evil LibDem Deep State. And it would also give them license in their minds to go after and repress transgenders or universities or other liberal groups to an even greater degree and with more open aggression than they currently are. That's why right-wing media like Fox and Trumper pols are so desperately playing the blame game right now.
And if, as they likely secretly fear, the shooter turns out to be another disgruntled right-winger like the registered Republican who shot Trump, it will cause their whole narrative of "liberals are behind all of the current political violence/liberals are the ones who are escalating hateful rhetoric" to collapse. So here we are.