What caused the SS Edmund Fitzgerald freighter to sink amid a violent storm on Lake Superior on Nov. 10, 1975, killing its 29 crew members, remains a point of debate and mystery a half-century later.

Theories range from the Edmund Fitzgerald striking a shoal and suffering bottom damage to flooding through the freighter's hatch covers, which filled the ship with water and sank it, to rogue waves, to structural flaws in the ship that the 1975 storm made deadly.

Fed investigations: Ship likely sank due to faulty, failing hatch covers

Two major federal investigations were conducted after the Fitzgerald's 1975 sinking: the U.S. Coast Guard's Marine Board of Investigation, which released its report in July 1977; and the National Transportation Safety Board, whose findings and recommendation

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