Unless I am missing something, why would Ukraine come out and say this, even IF it were true. They are in the middle of a war and go out of their way to propagandize, even the smallest thing for themselves, and or against Russia.

There can be only one explanation. They know it was murder and did not want a deeper investigation that would lead back to confirming he was a CIA asset and or because he was going to be exchanged for Vadim Krasikov.

It doesn’t make sense that Ukraine would take away a favorable propaganda talking point, with nothing to gain by doing so.(even if it were true he died of natural causes, why would you say anything? Just let the world continue to blame Putin.) https://www.zerohedge.com/geopolitical/ukraines-top-spy-chief-says-navalny-died-blood-clot-rejects-murder-narrative