Bolsheviks In the 1930s other senior Communists, many of whom had been Stalin's allies were removed and many of them were executed or died in mysterious circumstances, including Lev Kamenev, Grigory Zinoviev, Alexei Rykov and Nikolai Bukharin. Joseph Stalin instigated a series of purges against senior members of the party, culminating in the Great Purge of 1935 to 1938, with the key processes known as Moscow Trials. There are theories that purges were initiated as a tool in Stalin's struggle for power. At the 17th Congress of the All-Union Communist Party (b) (February 1934) Sergei Kirov only received three negative votes in the election to the Politburo showing himself to be the most popular Soviet leader while Stalin received 267 negative votes ranking him the least popular. According to Molotov's memoirs as well as other reports, a number of party members at the Congress had approached Kirov with the proposal that he run for the position of General Secretary against Stalin. Whether or not Stalin initiated the Purge as a response to opposition to him within the party and whether or not Stalin was personally behind the assassination of Kirov in December 1934 in order to remove a rival, that was used as a pretext for the Purge, the fact remains that of the 1,966 delegates who attended the 1934 "Congress of Victors", 1,108 were ultimately arrested by the secret police. Of 139 members of the Central Committee, 98 were arrested. Ostensibly, the purge began as an investigation into Kirov's murder. Zinoviev and his former supporters were charged with the murder and subjected to show trials before being executed. The "investigation" continued and soon found thousands of alleged conspirators who were similarly rounded up and shot or put into labor camps. Stalin claimed that Kirov's assassin, Leonid Nikolaev, was part of a larger conspiracy led by Zinoviev, Kamenev and ultimately Leon Trotsky against the Soviet government. Additional triggers for the purge may have been the refusal by the Politburo in 1932 to approve the execution of M. N. Riutin, an Old Bolshevik who had distributed a 200 page pamphlet calling for the removal of Stalin and their refusal in 1933 to approve the execution of A.P. Smirnov, who had been a party member since 1896 and had also been found to be agitating for Stalin's removal. The failure of the Politburo to act ruthlessly against anti-Stalinists in the Party may