The FBI encouraged these suspicions by planting fabricated evidence which suggested that many innocent Party members were FBI informants.[172] Dennis attempted to provide leadership from inside the Atlanta penitentiary, but prison officials censored his mail and successfully isolated him from the outside world.[3] Prison officials from the Lewisburg prison prevented Williamson from writing to anyone other than immediate family members.[135] Lacking leadership, the CPUSA suffered from internal dissension and disorder, and by 1953 the CPUSA's leadership structure was inoperative.[135][173] In 1956, Nikita Khrushchev revealed the reality of Stalin's purges, causing many remaining CPUSA members to quit in disillusionment.[174] By the late 1950s, the CPUSA's membership had dwindled to 5,000, of whom over 1,000 may have been FBI informants.[175]