The trial was coming to an end and Procurator-General Andrei Vyshinsky needed to make it clear that the result had already been determined. He stated “These mad dogs of capitalism tried to tear limb from limb the best of our Soviet land.” He continued “I demand that these mad dogs should be shot-every one of them!”
The result was already secured but to the Stalinist regime it was important to stage a trail. The two biggest defendants in this theatrical performance were Grigory Zinoviev and Lev Kamenev. Both were revolutionaries. They had been friends with Lenin. They had been in the Politburo. Both had worked closely with Stalin and helped advance his career. They were old Bolsheviks but now they had fallen out of favor with Stalin. At some point Stalin decided that they needed to die. A public show trial would provide the avenue to sentence them to their deaths.
The pretext for the trial revolves around the assassination of Andrei Kirov. Neither man played a role in the assassination but guilt had been predetermined. Now the organs of the state needed to secure confessions which Kamenev and Zinoviev had no inclination to give.
Simon Sebag Montefiore describes the following scene “Stalin’s office phoned hourly for news.
“You think Kamenev may not confess?”Stalin asked Mironov one of Yagoda’s chekists.
“I don’t know,”replied Mironov.
“You don’t know?”Said Stalin. “Do you know how much our state weighs? With all the factories, machines, the army, with all the armaments and the navy?”
Mironov thought he was joking but Stalin was not smiling.
“Think it over and tell me.” Stalin kept staring at him. “Nobody can know that Joseph Vissarionovich it is the realm of astronomical figures.”
“Well and can one man withstand the pressure of that astronomical weight.”
“No,”replied Mironov.
“Well then don’t come to report to me until you have in this briefcase the confession of Kamenev.”
Those responsible for securing the confessions did not resort to physical torture but they did use other means of torture including physiological methods including threats to family members.
To make the show trial even more spectacular Stalin added more conspiratorial charges. According to Montefiore Kamenev and Zinoviev were determined to be leaders of the “Terrorist leviathan named the United Trotskyite-Zinovievite Center,” which conspired to kill Stalin and 7 other Politburo members.
Kamenev and Zinoviev negotiated a meeting in front of members of the politburo and agreed that they would plead guilty if their lives were spared. Thinking that they had received assurances from Stalin that the death penalty was off the table they agreed to plead guilty. When the trial concluded they were sentenced to death and executed on August 25, 1936.
In the Soviet Union the rule of law resided in the hands of one man. That man was Stalin and on his order any punishment was justified for any person. The first show trial showed that not even old Bolsheviks were above the rule of Stalin’s whims.

Reference
Stalin the Court of the Red Tsar by Simon Sebag Montefiore