https://en.wikipedia.org/wiki/Nikita_Khrushchev#Involvement_in_purges
Beginning in 1934, Stalin began a campaign of political repression known as the
Great Purge, during which millions of people were executed or sent to the
gulag. Central to this campaign were the
Moscow Trials, a series of show trials of the purged top leaders of the party and the military. In 1936, as the trials proceeded, Khrushchev expressed his vehement support.
Khrushchev assisted in the purge of many friends and colleagues in Moscow
oblast. Of 38 top Party officials in Moscow city and province, 35 were killed
[40]—the three survivors were transferred to other parts of the USSR. Of the 146 Party secretaries of cities and districts outside Moscow city in the province, only 10 survived the purges. In his memoirs, Khrushchev noted that almost everyone who worked with him was arrested. By Party protocol, Khrushchev was required to approve these arrests, and did little or nothing to save his friends and colleagues.
Party leaders were given numerical quotas of "enemies" to be turned in and arrested. In June 1937, the
Politburo set a quota of 35,000 enemies to be arrested in Moscow province; 5,000 of these were to be executed. In reply, Khrushchev asked that 2,000 wealthy peasants, or
kulaks living in Moscow be killed in part fulfillment of the quota. In any event, only two weeks after receiving the Politburo order, Khrushchev was able to report to Stalin that 41,305 "criminal and
kulak elements" had been arrested. Of the arrestees, according to Khrushchev, 8,500 deserved execution.
....
In late 1937, Stalin appointed Khrushchev as head of the
Communist Party in Ukraine and Khrushchev duly left Moscow for Kiev, again the Ukrainian capital, in January 1938.
[47] Ukraine had been the site of extensive purges, with the murdered including professors in Stalino whom Khrushchev greatly respected. The high ranks of the Party were not immune; the Central Committee of Ukraine was so devastated that it could not convene a quorum. After Khrushchev's arrival, the pace of arrests accelerated. All but one member of the Ukrainian Politburo Organizational Bureau and Secretariat were arrested. Almost all government officials and Red Army commanders were replaced. During the first few months after Khrushchev's arrival, almost everyone arrested received the death penalty.