I believe Casso's version.
The contract was first given to Gotti who couldnt get close to him then to Frank DeCicco who couldnt get to Roy either, finally DeCicco went to Paul Castellano and suggested reaching out to Anthony Casso (who knew the Testa's).
A deal was struck where the Gemini twins would whack Roy and they would then go to work for Casso.
The Twins really didnt have a choice, when the boss of bosses wants someone gone you do as your told - if they hadnt killed Roy then they would have been killed themselves.
Roy supposedly went to a meeting at Patty Testa's house where he let his guard down as he felt safe amongst 3 of his best men.
He was seated and about to recieve coffee when Joey and Anthony opened fire.
Albert Demeo later said his father had a hole in his hand which suggested Roy saw it coming and threw his hands to cover his face in a final futile act.