Lord Blackwood seem to reappear because: Blackwood is not in his tomb, leading to the belief that he has risen from the grave.
Lord Blackwood was the main character in the novel "Sherlock Holmes". He was known as a ritualist and often use human being as a sacrifice.
Lord Blackwood reappear to the police officers on the scene based on the fact that he was not found in his tomb which inturn lead to the belief that he has risen from the grave.
Therefore Lord Blackwood reappear because he is not in his tomb.
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