Every single German from the top generals both army and SS right down to privates and even telephonists and machine operators of the ventilation system tell exactly the same story even under harsh Russian interrogation over many years, one of them would have cracked and said he got away but they didn't
Stalin ordered a thorough investigation headed by the KGB, it lasted years and spread all over the world and their conclusion was he died in the bunker, they took his remains and buried them in Shoenebeck near Magdeburg on 21st February 1946 in an operation codenamed "The Archives"
Magdeburg came under East German juristriction in 1970 so to avoid the burial site becoming known the then KGB head Yuri Andropov ordered the remains dug up and incinerated and thrown into the Biederitz river
The Soviets kept 2 parts of the body, part of the cranium which is kept in the State Archives and part of the jaw bone which is kept in a vault at the FSB Archives