Horowitz had nothing to do with the Greenwich Village bombing and was long gone from New York by the 60s - in London and Berkeley by then. The thing about Horowitz - like Jane Fonda - is that both of them were in their 30s by the radical 60s when all the rest were “kids”.
Abbie Hoffman, at 32, was the OLD MAN, telling the stupid kids "DON'T TRUST ANYONE OVER THIRTY" and the STUPIDS cheered! MORONS!
Mark Rudd was 30, Rennie Davis was 27, Angela Davis was 24, Tom Hayden was 29, Dohrn was 26, Ayers ( who had a different girlfriend back then, who was the LOVE OF HIS LIFE and was blown up nicely ) was 24, Kathy Boudin was 24 or 25, and Cathlyn Wilkerson was 23 and yes, I looked up all of their B-Days, to make sure that my info was correct. :-)
Horowitz wasn't in NYC, in the late '60s; however, he WAS a part of the stinking MARXISTS and they LOVED his writing. He was also BFF with Huey Newton and wrote glowing crap about the BLACK PANTHERS ! IIRC, it's probably these writings, of his, that first alerted me to Horowitz, way back when. And he also probably appeared as a a signatory, in at least one of the stupid double page "letter" ads that were published in the N.Y. Times. I'd have to check my "ENEMIES LIST" ( I would write down all of the names, when there were such things, as well as who was in the news and still have those lists somewhere. ) to make certain, though.