An FBI agent applied for a federal warrant in 2018 to seize a cache of gold that he said had been “stolen during the Civil War” while en route to the U.S. Mint in Philadelphia, and was “now concealed in an underground cave” in northwestern Pennsylvania. That’s according to court documents unsealed Thursday. The FBI had long refused to confirm why exactly it went digging on state-owned land in Elk County in March 2018. Federal authorities say the dig came up empty. The FBI said in the newly released court documents that it feared the state of Pennsylvania would claim the gold for itself, setting up a costly legal battle.