[Jan-Poo]

Originally Posted by Will Wright

As for Will's "A coffin is not a locked room" I thought it was a reference to one of Ellery Queen's novels, that has almost the exact same quotation.

Spoiler:

Ellery:"Explain the locked room? Why should I? A coffin is not a locked room."

That referred to the victim not dying inside the locked room itself, but being moved after his death. It was where the victim was supposed to be after dying. In other words, every victim had a perfect alibi if the victim died when everyone thought he did. But he died at a different time, and the coffin was what made the room seem impossible.

Ellery goes on to deduce who the criminal is based on that, and chases after the criminal.

Then he explains the trick involving a fake key in order to explain how the murderer made it seem like the room was locked even though the key he found was not the one used to lock the door.

It's a complex trick.

So yeah, that's what I took it as. Almost all of Will's responses were, word per word, a quotation from some Golden Age detective. I just automatically assumed the same tricks were used for those locked rooms as the locked rooms/quotations were very similar.

This is interesting. Considering this, it is possible that Will's answer doesn't have a meaning by itself.
What Will tried to do was to provide a proof that he solved the mysteries without telling the truth explicitly. The reason is that telling the truth hurts Beatrice (as we have seen in EP4 and EP5), so Will used the most merciful method (he didn't even use blue).

That however was only possible through a certain "code" that he and Beatrice would understand. Will as an inquisitor must certainly know the mystery genre and its canons, Beatrice is also an expert, so probably Will took for granted that Beatrice read Ellery Queen.

If my reasoning so far is correct, then what Will wanted to tell to Beatrice is: "You used the same trick Ellery Queen used in that book".

Now I only need to understand how exactly that can work in umineko.
The victims or one of the victims didn't die inside that room?

I don't get it...
Will can you tell us more about that closed room? Maybe the trick is not related to the bodies... how exactly was the closed room created?