That, and the Ukrainians wouldn't know who ordered the job beyond their Control Officer.
He was much more subtle than the atomic bomb but Stalin saw him as no less deadly.
Ahem. In 1943, there was no such thing as an A-bomb. There were programs in the US working towards one (heavily infiltrated by Soviet spies), but nobody had any idea whether it would really work.
Who was more likely to have been a German agent rather than a Soviet one. But then again, Old Uncle Joe was probably a few beets short of a borscht by 1943, so almost anything is possible.