The 5th card of The Dead Man's Hand

The hand Wild Bill Hickok held when he was shot in now called The Dead Man's Hand.

Ace of spades Ace of clubs 8 of spades 8 of clubs with either a 9 of diamonds or a 5 of diamonds.

Nobody knows for sure what the 5th card was. I don't like unsolved mysteries so I am going to try to prove it logically one way or the other.

The Dead Man's Hand is sometimes depicted like this but I never hold a poker hand this way.
I hold it like this with the useless card in front to conceal the 'good' cards from peekers.
Also, once I know what is in my hand I no longer hold it fanned or, at least, I hold it close to my chest. Wild Bill Hickok was a good poker player and I am sure he would hold his cards this way, too. He would take care to conceal his Aces and 8s from anyone standing behind him who might wish to signal what he was holding to one of the other players. The only card they might see would be the useless card. The fact that he was shot in the back of the head shows that there was someone behind him.

Now, about that 5th card.
Could a 9 be mistaken for a 5? I don't think so. There are simply too many red diamonds scattered over the face of a 9 and not very much white space. I think it is not possible to mistake a 9 for a 5. So, if the 5th card was a 9 it seems highly unlikely that the possibility of it being mistaken for a 5 would ever arise.

What about mistaking a 5 for a 9? Can a similar argument be applied to show that it is not possible to mistake a 5 for a 9? A 5 has much more white space so that would seem to eliminate a 5 or 9 confusion. That argument, however, fails to take into account a very important point: When Hickok was shot he would have slumped forward and blood from the wound could easily have dripped onto the card and changed its appearance.

If a drip of blood covered the region near the top right of the 5 it could easily have made the 5 look like a 9. That would not have caused confusion to those who saw the hand at this stage because it would still be possible to distinguish the pips from the blood splatter and so recognise the card as the 5 of diamonds.
However, if the cards had been picked up and reassembled to display the hand, with the Aces and 8s put on top of the unimportant 5, then its pips can no longer be seen. All that can be seen is the 5 defaced into a 9 by a bloodspot. Some of those seeing the hand this way might mistakingly think the 5th card is the 9 of diamonds.
Of course, it might be claimed that if the card had been a 9 it could have been splattered by the blood precisely as is suggested for the 5. But consider this: Could those looking at a 9, blood splattered on not, mistake it for a 5? That is hard to imagine, simply because a 9 would only ever look like a 9 and never like a 5 and not to be mistaken for a 5. If it had been a 9 then the question of whether it might have been a 5 would never have arisen. The mere fact some people say it was a 5 is of itself almost enough proof that it was not a 9. It would seem that those who said it was a 9 have misread it for the reasons stated above.

The odds favour 5 of diamonds being the 5th card.