A jailhouse tip led investigators to the farm where they dug up a small area Saturday but found no trace of Peterson, who disappeared in 2007.
"We've been down different paths before and there have been disappointments before," said Illinois State Police Master Sgt. Tom Burek. "I don't want to stand here and tell you this is the magical lead that's going to solve the case."
Police visited the 150-acre alfalfa farm outside Peoria after a jail inmate urged them to search near a gun club in downstate Illinois, a source told the Chicago Tribune. Authorities narrowed it down to the farm, which is owned by a man who said he did not know suspect Drew Peterson and was stunned when detectives contacted him.
Drew Peterson, a former Bolingbrook, Ill., police sergeant, is in jail charged with killing his third wife, Kathleen Savio, in 2004. He has denied any role in the subsequent disappearance of his fourth wife, Stacy.