It was Fred "Killer" Burke. And yes, McGurn planned and organized the hit but wasn't present at the hit.
Q. Who were Bugs Moran's top gunsels?

Ntra la porta tua lu sangu � sparsu,
E nun me mporta si ce muoru accisu...
E s'iddu muoru e vaju mparadisu
Si nun ce truovo a ttia, mancu ce trasu.