 If you liked
Umineko no Naku Koro ni
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 ...then you might like
Kubikiri Cycle: Aoiro Savant to Zaregotozukai
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With setting that is a separate island, mysterious murder happens and police isn't an option, so it's up to the cast to figure out the culprit with the confusing clues they got. Both anime have some nice locked room mysteries.