Possible fued between Sollecito and Scoppa? Always intriguing to speculate, but perhaps it's much less interesting and it's all about an unpaid debt. I may misremember, but I thought Salvatore was in trouble with street gangs. There was a price on his head before this war started.
Anyway, with Andrew incarcerated his brother probably has to step up, if he hadn't already.
"It was between the brothers Kay -- I had nothing to do with it."