I just found out what R’ Elyakim Shlesinger actually claimed…
Some anti-Zionist rag (quoting Schleisinger’s Hador V’Hatekufa, p. 67):
“… Rav Elyokim Schleisinger recalled that the doctor who treated Rav Blau on the ship was certain that he had been poisoned. However, Rav Dushinski instructed the family not to open a criminal investigation. In fact, it is said that Rav Blau himself was aware of the threat and ate only from his own food throughout the journey, but made an exception for that cup of tea, which was indeed poisoned.”
(Of course, Rabbi Shlesinger’s word, if unbacked by others, is worthless. He’s a well-established liar.)