[Taynis]

Originally Posted by Jan-Poo

He, nice question. The anime never really covered that, but at the end of Ep1 in the VN basically it is said:

Spoiler for VN episode1:

The police finds a very gruesome scene. There are pieces of bodies everywhere, they are able to confirm anyone's identity except for the four cousins, however after they find a piece of Maria's jaw they lose any hope that they are still alive.

After that the incident is being known as Rokkenjima serial murder incident,

Then a message in a bottle was found describing how the people on rokkenjima died in a sort of ritual to revive the witch Beatrice. The signature says Ushiromiya Maria (the rest was told in the anime)

Then Ep2 and Ep3 don't say much except for Ep3 tea party which however can be considered an anticipation of Ep4.

I'll write what can be understood from Ep4 about what the police has found. mind that some things might be said in the next anime episode, however there's nothing really relevant to the plot.

Spoiler for VN episode4 on what the police has found:

The topic is always avoided. But from how the people act and say it can be understood that

Officially the police never considered the Rokkenjima incident a crime. Everyone uses the neutral word "incident", and it is often referred as an "unfortunate incident".

There is however no actual mention of what was discolosed to the public. And differently from Ep1, here they don't say a thing not even a hint on the conditions of the bodies. The only thing that we know for sure is that Nanjo's body wasn't found.

Eva has been found in Kuwadorian, but little is said about how they have found here there and why she was there. Eva refuses to explain what happened. There is nothing that would make think that she was suspected by the police or that she underwent a trial.

However two years later a message in the bottle was found by a fisherman (same thing as in Ep1), but here in Ep4 we learn that the police already had found another one on the day of the incident. Both are signed "Ushiromiya Maria" but it is confirmed that it isn't Maria's handwriting.
The messages however seem reliable because everyone that has been in the island by reading them can understand that whoever has written them has a very good knowledge of the island and the Mansion.

Because of that letter and because Eva became a bitch hated by everyone rumors started spreading that Eva killed all of her relatives. Talk shows and magazines began to talk a lot of this mystery and that's how the legend of the "Rokkenjima serial murder mystery" born.
So much uproar was raised that the case was reopened and a more deep investigation was done about Eva and her involvement in a spossible crime. However nothing suggests that they have found anything on her.

Ah, the professor Ange meets in the restaurant (Ootsuki) says that a lot of very rare books from Kinzo's collection were auctioned by Eva around two years after the incident. It was explained that the books escaped the disaster. It seems that they all came from Kuwadorian, and not from the Mansion.

That's pretty much all that is known so far.

Originally Posted by Arbane the Terrible

The first sound-novel has an epilogue at the end. It's a little vague on what the police found, aside from the childrens' bodies being so utterly destroyed that they were lucky to find enough of a jaw fragment to positively ID Maria.

One theory I've heard is that the island was hit by a tsunami or the mansion collapsed in a landslide, either of which would probably cover up most of the evidence of any murders having been committed, and would help explain why Eva survived the third arc (hiding in Kuwadorian). But it doesn't explain how she knew to hide there...

Thanks for the answers, I'm very curious about the bodies and all