The Gates of Europe: A History of Ukraine by Serhii Plokhy:
Yaroslav died on February 28, 1054, and was buried in the Cathedral of St. Sophia, which he had built. His earthly remains were placed in a white marble sarcophagus decorated with carvings of the Christian cross and Mediterranean plants, including palms, which were by no means native to Kyvian Rus’. According to one theory, the sarcophagus—a stone embodiment of Byzantine cultural imperialism—had once been the final resting place of a Byzantine notable but was brought to Kyiv either by marauding Vikings or by enterprising Greeks. The sarcophagus is still preserved in the cathedral, but the remains of Yaroslav the Wise disappeared from Kyiv in 1943, during the German occupation of the city. By some accounts, they ended up in the hands of Ukrainian Orthodox hierachs in the United States and were spotted in Manhattan after the war. Some suspect that they may now be in the Church of the Holy Trinity in Brooklyn.
What could account for the transfer of Prince Yaroslav’s remains all the way to the Western Hemisphere? The answer has nothing to do with American cultural imperialism but is closely associated with the Ukrainian claim to the legacy of Kyivan Rus’. Ukrainian clergymen leaving their homeland removed the relics so as to prevent them from falling into the hands of the advancing Soviet army. Concern that if returned to Kyiv, they might end up in Russia explains enough the continuing refusal of the custodians of the Brooklyn church to discuss the issue of Yaroslav’s remains with representatives of the Ukrainian government.