Nonetheless, he played a role in prosecuting members of the Communist regime apparatus for harsh crackdown against pro-democratic protesters during the Velvet Revolution.
[5] In addition to leading prosecution of the former communist officials, Trnka launched investigations against personnel of the secret service agency SlS accused by the political opposition of destroying evidence possibly implicating members of its communist-era predecessor StB.
[7] As a prosecutor general, he was associated with an informal, frank approach to communication and wearing casual clothing in the office, that had been previously dominated by lawyers in suits using the professional jargon.
The key proof was a recording found in the possession of the arrested businessman Marián Kočner, who had installed a hidden camera in Trnka's office.
The recordings also show that Trnka had in his possession key evidence for the Gorilla scandal, which he used to blackmail the businessman Jaroslav Hasčák.