i dont think there are any heavy mysteries about the decline of them furio. heavy prosecution, admin member/acting boss cooperating, old age, reluctance to induct new members, sitting boss imprisoned for a long stretch with no intention to give up the throne ( this has long been a problem especially for ny families), those members on street not being able to start or expand new rackets outside a small geographic area and no interest in parterning with other non mafia crime groups. also infighting which goes back to riggis holding on to boss position. riggi installed a 3 man panel that did not get along and tried to take each other out. the decavs basically suffered the same reasons for decline as every other north american crime family, because of there already and historical small membership only made the decline faster. with it decline any prospective members from an already small pool in the state of new jersey likely went with one of the other top 3 families in the state; genovese, lucchese and philadelphia.