http://m.levittandkaizer.com/upload/DEFILIPPO%20BRIEF%20FINAL.pdf

Guys... I found a court document and took out some excerpts that may clarify as to the motive of Sciasca's murder.

Page 14:
Vitale, for his part, was jealous of anyone who got too close to Joe Massino
(5168-69), and Sciascia was on Massino’s ruling Committee, thereby posing
a threat to Vitale’s plan to some day ascend to the pinnacle of power in the Bonanno family.

page 15:
Vitale (3453). At the same time, Vitale would likely have seen Sciascia as a
potential threat not only to his standing with Joseph Massino, but also to his
life, as Sciascia – reputedly a large-scale drug dealer – was himself
responsible for numerous murders.
Additionally, Vitale was certainly in a position to falsely accuse Mr.
DeFilippo of the Sciascia murder and motivated to do so.

Page 16:
Vitale testified as follows: Massino had spoken to Vitale at a social
gathering and asked Vitale to supervise the murder of Sciascia, who Massino
supposedly wanted killed because Sciascia had accused Massino’s friend,
Anthony Graziano, aka “TG”, of having a drug problem (2796-97, 2799-2802).