All the three Moscow trials of 1936-1938 against various real and imagined opposition members (the case of the Trotskyite-Zinovievite Terrorist Center in 1936, the case of the Anti-Soviet Trotskyist Center in 1937 and the case of the Anti-Soviet "Bloc of Rights and Trotskyites" in 1938) were carefully orchestrated by the NKVD, and as they constituted one interconnected series, I will also speak of the participants of the other trials, as these trials stand or fall together.

That the trials were staged was confirmed already in Stalin's time, as some of the organizers (like Frinovsky and Yezhov) were arrested themselves and provided some revealing information during the interrogations. For example, in a statement of M. P. Frinovsky to L. P. Beria dated 11.04.1939, attached to the special message of Beria to Stalin dated 13.04.1939, Lubyanka. Stalin i NKVD-NKGB-GUKR "Smersh", 2006, pp. 47-48, we read:

How were those arrested prepared for face-to-face confrontations, and especially face-to-face confrontations, which were conducted in the presence of members of the Government?

The arrested persons were specially trained, first by an investigator, then by the head of the department. The preparation consisted in reading out the testimony given by the arrested person to the person with whom the confrontation was to be carried out, explaining how the confrontation would be conducted, what unexpected questions the arrested person might be asked and how he or she should respond. In essence, there was collusion and a rehearsal of the forthcoming confrontation. After that, the arrested person was summoned by EZHOV or, pretending that he accidentally walked into the investigator's room where the arrested person was sitting and was talking to him about the forthcoming confrontation, asking if he was feeling firm, whether he would confirm and, by the way, inserting that members of the government would be present at the confrontation.

Usually EZHOV was nervous before such face-to-face confrontations, even after talking to the arrested person. There were cases when an arrested person while talking to EZHOV made a statement that his testimony was not true, that it was a lie.

[...]

Preparation of the trial of RYKOV, BUKHARIN, KRESTINSKY, YAGODA and others

Actively participating in the investigation in general, EZHOV withdrew from the preparation of this process. Before the trial there were confrontations of the arrested, interrogations, clarifications, in which EZHOV did not participate. He talked to YAGODA for a long time, and this conversation concerned mainly the YAGODA's belief that he would not be shot.

EZHOV spoke several times with BUKHARIN and RYKOV, and also assured them in order to calm them down that they would not be shot in any case.

[...] As for the poisoning of EZHOV. The idea of his poisoning was put forward by Yezhov himself - day after day stating to all the deputies and heads of departments that he feels bad, that as soon as he stays in the office, he feels some metallic taste and smell in his mouth. After that, he began to complain that his gums started to bleed and his teeth started to loosen. EZHOV began to say that he had been poisoned in his office, and thus inspired the investigators to obtain evidence, which was done with the use of the Lefortovo prison and the use of beatings.

Various methods were applied to various accused, some were not tortured physically but only coerced psychologically (threats to family, etc.). Sometimes both torture and psychological methods were applied.

One of the accused (Krestinsky) actually initially did not admit his guilt in court, despite the fact that earlier he had been brutally tortured. An ex-NKVD man Aronson later testified about what happened next (from the head of the KGB I. A. Serov's note on the trial of the "Anti-Soviet Right-Trotskyist Center" from 07.07.1956, sent to V. M. Molotov on the same date, in Protsess Bukharina. 1938 g. Sbornik dokumentov, 2013, pp. 852-858):

During the break, we, the investigators, discussed what had happened and discussed how to get out of this situation. NIKOLAEV (leading the case of RAKOVSKY) then said that he would try to settle the incident. When the defendants were being taken from the court, KRESTINSKY was taken along with RAKOVSKY. The next day, KRESTINSKY confessed guilt and confirmed all his earlier testimony. I think, and so said the investigators afterwards, that Krestinsky was not beaten, but persuaded by RAKOVSKY. They said that RAKOVSKY, who had a great influence on KRESTINSKY, told him something like this: "You have to admit guilt, everybody admits guilt, and a non-repentant will be seen by the court as an unrepentant enemy, and will be shot, while a confession will save your life. The family of the confessed person will not suffer, and if you refuse, they will also be repressed. This has had such an impact on KRESTINSKY that he did not try to retract the evidence given during the investigation until the end of the trial.

We learn a bit more about the psychological tricks of the NKVD from the accused Rakovsky (ibid.):

Rakovsky himself told in the Orel prison cell as follows about the situation during the investigation into his case, as can be seen from the report by agent "Dima": “... when they make it clear to you from the very first day that you should lie about yourself and about the others, dirty your name and honor, then you are seized by rage, indignation. You begin to fight, to resist, but then, when they tell you, as ARONSON said: “Old man, you will give in, give evidence”, when you are told that your family will be destroyed, that you will be shot, you give up. When they told me that my wife would be put in Lefortovo, I screamed and grabbed my head - it meant that she would die. Fear for the family, the understanding that you are sending it to death, fear and the desire to live, complete hopelessness, and then party automatics, the habit of obeying the party - make you lie and do the devil knows what. All this is a lie, here in all these cases there is not a drop of truth ”, (arch. case No. 300956, vol. 9, p. 321) .

Nobody except Krestinsky openly retracted confessions during the trials. However those whose lives were temporarily spared (Pletnyov, Rakovsky, Bessonov, Radek, Sokolnikov, Arnold, Stroilov) unanimously testified about the staged nature of the trials, which is why they were soon murdered one way or another. We know this first of all from the contemporary NKVD documents (the prison "agents" were writing reports about their talks with the inmates in which those retracted confessions), from their own letters (e. g. Pletnyov wrote quite a lot before he was shot) and from the post-1953 investigations. Bukharin was not spared, but he retracted his confession in his 10.12.37 letter to Stalin. Various versions of the drafts of the "last words" of some of the accused were found in the NKVD files.

I haven't yet seen *direct* evidence specifically about Kamenev and Zinoviev, but the fact that the whole trials were faked is established, so their confessions are also necessarily false. I think this description by one of the prosecution's own witnesses, Kamkov, is a good summary (cited from Serov's note referenced above):

Another witness of the prosecution who testified in the case of the anti-Soviet bloc, former member of the Central Committee of the Party of the Left Socialist Revolutionaries B. D. KAMKOV, as seen from the testimony of the arrested BRYUKHANOV, who was held with him in the same cell, told him:

"All three recent trials were as much blackmail as the previous ones. There is not a single drop of truth in them. Neither ZINOVIEV nor BUKHARIN had any counter-revolutionary conspiracy work. Espionage, diversions, sabotage, terror, killing are all lies fabricated by the NKVD. Testimony was obtained from the accused through torture, blackmail, beatings, threats, threats to kill their families, arrests of wives, etc., by means of physical and mental coercion. At the same time, means of bribery, mollifying of the accused were used, life was promised, etc...". (arch. case No. 967389, separate package).

After the end of the trial of BUKHARIN and others, KAMKOV was tried on charges of joining an illegal terrorist organization in Arkhangelsk and spreading "heinous defamation in connection with the trials of right-wing Trotskyites in prison".

On August 29, 1938, during the consideration of the case in the Military Collegium of the Supreme Court of the USSR, KAMKOV didn't find himself guilty of anything and was sentenced to execution.

Perhaps an even better one, referring to all three trials, is contained in the note of the Commission of the Central Committee of the CPSU, consisting of V. Molotov (Chairman), K. Voroshilov, L. Kaganovich, M. Suslov, N. Shvernik, E. Furtseva, P. Pospelov, A. Aristov, R. Rudenko to the Central Committee of the CPSU, dated 10.12.1956 (in Reabilitatsiya: kak eto bylo, vol. 2, 2003, p. 207):

In reviewing the materials of the remaining trials listed in the present note, the Commission found that the charges of treason, espionage, terror, preparation and execution of the murder of S.M.Kirov, brought against the convicted persons, were not proved by the case materials.

Testimony on the merits of these charges with a confession of guilt was obtained from the convicted persons as a result of the application of illegal methods of investigation to them: deception, blackmail and measures of physical coercion.

I have translated numerous Soviet documents confirming the staging of the trials and posted them here: https://holocaustcontroversies.blogspot.com/2019/08/again-about-stalinist-deniers-yes.html