Much of the evidence for Hitler's death comes from eye witness testimonies and recently Soviet archives that have been declassified. There was quite a few people who while they didn't witness Hitler actually physically pull the trigger, did hear the gunshot and saw the bodes being taken away.

Here is the testimony given by his secretary Gerda Christian:

I learned from Linge (Hitler's driver) that he, together with Borman and Kempka had carried the bodies into the garden where the cremation was still in progress....I once again went into Hitler's living room-cum-office. There I saw a bloodstain about the size of a hand on the rug next to the sofa.

This is in addition to the testimonies of Hitler's personal attendant, his chauffeur, and other ss personnel present.

Here is Hitler's personal attendant, Otto Gunsche had to say after entering the area where Hitler had shot himself:

Eva Braun was lying on the sofa....the head was on the left side of the sofa, she was lying on her back with her legs drawn up slightly....Hitler himself sat in an armchair standing to the left and slightly forward... his body was slightly sunk together and slanted slightly to the right over his armrest.

Now I should mention that Gunsche was incorrect in the placement of the body. As Hitler was actually on the sofa with Braun, hence the bloodstain being near the sofa. The testimonies on the positions of the bodies vary among the three who actually saw them and lived. The other two who saw were Artur Axmann and Heinz Linge. The reason for the testamonies being different is unknown, but is speculated that they simply didn't register the positions correctly and they only remembered when they were interrogated.

Now a lot of the myths about Hitler's death are due to the awful way in which the Soviets cataloged it. A KGB doctor who wrote books about the death of Hitler, Dr. Bezemensky, began to spread myths about the death of Hitler around the 50's. He claimed that the photographs the Soviets took of the corpse on May 4th were faked, and he also began to spread the very popular myth that Hitler took cyanide poison before dying.

Also, it would have been pretty much impossible for Hitler to escape Berlin, it was surrounded by Soviet troops and it would have been near impossible to avoid detection. Borman tried to escape but was unable to find a way past the Soviets. So the likely hood of Hitler being able to is very slim.

Source:

Hitler's Last Days by Anton Joachmisthaler.

Question to historians - Is there any proof at all that Hitler and Eva escaped via submarine and emerged in South America, and ended up residing in Argentina, or another South American country? I hear this time and time again.. and read declassified intelligence papers of it, but it's not the official story?

edit - google "declassified hitler argentina" and read the FBI files yourself then. I'm just saying, is there any other tangible proof? Why downvote and not answer?

This book is written by Hitler's Valet and talks about his life right up to the dying days, don't know if he was actually around at the very end though (not got that far). Does anyone know? http://www.pen-and-sword.co.uk/With-Hitler-to-the-End/p/3903/

Update I just found the following quote "In the midst of the deafening cacophony of exploding artillery shells, a pistol shot rang out in Adolf Hitler's bunker complex. I did not hear it myself, but as the oder of the gun discharge drifted through the door frame I knew that Hitler has shot himself." There's actually a whole chapter on the suicide with transcripts.