Can I ask what this is based on?
Hitting multiple members of another family almost certainly cannot be ignored.
If it was one guy who committed a serious infraction it may be turned a blind eye, but the Lukes attempting to hit multiple members of another family would almost certainly demand reprisal and an ensuring war.
I find it very hard to believe they would willingly start a war in this day and age and risk their construction/union success. All predicated by a slight.
I would think Crea smarter than that.
We know that Stagno was the target of a rubout attempt by the Lukes. It therefor follows without any other evidence that he was the one who committed the transgression and logically the one referenced in the latter Cassano attempt.