What is certain is that he was last seen alive with Lucchese soldiers Peter "Rugsy" Vario and Bruno Facciola whom he thought were taking him to the place where he was going to be inducted.

My opinion is that he was killed by the Luccheses. Not necessarily by these two guys but i believe the whole thing was done by the Luccheses (from him being taken to the place, the shooting and then the disposal of the body).

Another version is that Gambino soldier Tommy Agro did it. The Luccheses would have let the Gambinos do the killing because DeSimone had previously killed a Gambino made guy (William "Billy Batts" Bentvena). I find it hard to believe because that's not how mob hits usually happens : one family bringing the guy to a place and then another family shooting him dead. It doesn't work like that.

I know there are cases of guys being killed by another Family with the approval of their own Family (Gerry Pappa, John Simone,...) but I don't know any case of a "two-families hit".