In 1951, extensive purges were carried out at the ministry to prove the connection between the security forces and the alleged conspiracy within the Communist Party.
Deputy Karel Šváb and StB Commander Osvald Závodský were executed, with whom several other persons from the ministry were sentenced to many years in prison as part of the alleged Trotskyist - Zionist group organized by Rudolf Slánský.
The state security monitored public sentiments (for example, the reaction of the masses to the Slánský trial), identified and persecuted real and potential opponents of the regime.
On January 23, 1952, the leadership of the MNB was changed; Ladislav Kopřiva was dismissed, and the secretary of the Communist Party of Slovakia Karol Bacílek, a participant in the repressions against “Slovak bourgeois nationalists,” ( the case of Gustáv Husák and Vladmír Clmentis) one of the key organizers of the Slánský trial, was appointed.
His first deputies were the Slovak functionary General Oskár Jeleň, (previously the head of the political department of the Czechoslovak army) and Antonín Prchal who was one of the key organizers of the Slánský case.