Dan Rottenberg, who penned an award-winning biography on Slade, hired a radar company to scan the earth and find the casket, hoping to fulfill Slade's wife's long-ago wish to have his body moved to his hometown of Carlyle, Ill.
An August search turned up nothing, and Rottenberg had to wait until winter thawed before searching again. That search resumed last week with a stronger radar, but again the technology turned up no anomalies, other than the sprinkler system.
"Adam Kubicki of Ground Penetrating Radar Systems Inc., who conducted both scans, believes his equipment would have detected a casket if one were there," Rottenberg said in an e-mail Thursday. "But the cemetery records show that Slade is indeed buried in that area."
So for now, Slade's remains will stay shrouded in mystery and lost to time.
"I will continue to explore alternative technologies that might be capable of exploring underground without disturbing the soil," Rottenberg said. "Perhaps the best we can hope for is that some more advanced technology will be developed, preferably before I wind up alongside Jack."
Slade nourished an outsized reputation as a deadly shot and a zealous law enforcer who was responsible for 26 killings. In truth, Rottenberg says, Slade was only proven to have killed one man.
However, he relied on the power of tall tales to keep criminals at bay along the treacherous stage coach routes from Fort Kearny, Neb., to Salt Lake City.
"Slade was never one to be daunted by impossible odds, and I intend to follow his example," Rottenberg said.
Rottenberg credits Slade with helping launch the Pony Express, restoring the peace in a perilous region, and delivering the West's great riches to the Union ahead of the coming Civil War.
But for all his uncommon exploits, Slade had a common failing. He was fired for drunkenness and spent his final days as a regular bully in the Montana mining town of Virginia City. A particularly lurid spree prompted a local commission of vigilante settlers to lynch him on March 10, 1864.