Jimmy Hoffa's mysterious disappearance remains a mystery. Police in Roseville, Michigan, say their much-ballyhooed dig for the former Teamsters boss has turned up nothing, reports CBS Detroit. Acting on a tip, police dug up the concrete beneath a driveway shed in the Detroit suburb, but soil samples turned up no sign of human remains, the department announced today. As far as this tip goes, that means the case is closed. (More Jimmy Hoffa stories.)