In March 1937, the four main statistical professionals working on the Census in TsUNKhU – the chief of the Sector for Population, Mikhail Kurman; chief of the Census Bureau, Olimpiy Kvitkin; his deputy, Lazar Brand; and the chief of the Sector for transportation and communication, Ivan Oblomov, were arrested and imprisoned. Soon they were joined by the Chief of TsUNKhU, Ivan Kraval, and the chiefs of most of the regional statistical centers, and executions followed

https://en.wikipedia.org/wiki/1937_Soviet_census