Sciascia wask killed because he was siding with Vito Rizzuto over the Bonannos on issues. After the law enforcement crack downs in America the Rizzutos just became more and more independent and there wasn't really anything Massino could do about it they had their own problems going on. Massino had asked Rizzuto to send down a hit team to kill Robert Perino and he refused, thats when tensions started and Sciascia was the main meditator between Rizzuto and the Bonannos, but he sided with Vito on certain issues and accused Graziano of being high on drugs, so in 1999 Patrick DeFilippo shot Sciascia in the head in John Spirito's SUV