While the Zenit was being developed, there was major discord within the UPTI. The radio-location work at the LEMO was conducted in great secrecy, and other units of the UPTI objected to the lack of "freedom of scientific knowledge". It was also learned that LEMP scientists were paid substantially more than other UPTI professionals. This resulted in a push to have LEMP become a totally separate organization. At this same time, Joseph Stalin 's Great Purge swept the nation, and the UPTI was a target. Many persons were arrested under charges of sabotage and two were executed by a firing squad. Slutskin and his LEMO staff, however, remained safe and turned to converting the Zenit to a new, improved system.