The National Missing and Unidentified Persons System estimates that there are roughly 90,000 missing persons in the United States alone at any given time. While scientific advancements such as genealogy testing have solved many of these mysterious disappearances, many more remain unsolved — and will likely remain so.

Indeed, not all families will receive any semblance of closure. The family of Madeleine McCann, for example, has been searching for clues in their toddler’s unsolved disappearance for over a decade.

The lack of evidence in some of these missing persons cases not only hinders the investigation, but leaves a lot of room for conjecture, speculation, and conspiracy. The ominous disappearance of an Australian pilot in 1978, for example, has led many to blame aliens.

The most chilling unsolved disappearances below involve a broad range of shadowy entities, from the Italian Mafia to secretive Satanic worshippers, and they have implicated some of the world’s most powerful people.