Castle. Someone kills guests using hidden tunnels. Exposed in the end

Movies
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Castle owner uses hidden tunnels of his castle to come to bedrooms of his guests at night to kill them.
Journalist or someone else finds hidden room in the end of the movie, exposes the killer.
Watched this movie in 1990s.

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“Der Würger von Schloss Blackmoor” (1963), also known as “The Strangler of Blackmoor Castle”?

The story is somewhat similar, and there is a reporter at the end, but I think he is the killer.

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