SCOTT CITY, Mo. (AP) — Investigators in southeast Missouri dug for evidence this past week hoping for clues in an unsolved crime from four decades ago, but once again, they came up empty.

The Southeast Missourian reports that it was the latest disappointment in the 40-year-old disappearance of Cheryl Ann Scherer, a cold case that has baffled law enforcement and left Scherer's family struggling to find closure.

The Scott County Sheriff's office said little after the dig on Monday, other than the focus was on a field near a county road. The sheriff's office, the FBI and the Missouri State Highway Patrol all participated.

"Unfortunately, nothing was located during the search," the sheriff's department said in a brief news release, which didn't disclose what prompted the dig at that location.

Diane Scherer-Morris, Scherer's sister, said the investigation did not occur on "our family farm or any relative's farm."

Scherer was 19 when she disappeared from her job at the Rhodes Pump-Ur-Own gas station in Scott City the morning of April 17, 1979. Authorities believe Scherer may have been kidnapped.

During the initial investigation, co-worker Debbie Hamilton said she drove by the station at about 11:30 that morning and saw Scherer on duty. When Hamilton returned minutes later, Scherer was gone. Hamilton found Scherer's purse inside and her car parked outside. Also missing was about $480 from a bank bag in a desk drawer.

No witnesses to any crime have been located, though two people told authorities they saw a white Ford compact car at the station's pumps at around the time of Scherer's disappearance. One man was inside the vehicle and two others were standing outside.

The FBI and the sheriff's department have pursued hundreds of leads in the years since the disappearance. One of the more promising leads surfaced in 1984 when authorities in Florida and Texas arrested Otis Toole and Henry Lee Lucas who were subsequently convicted of random killings as they traveled the country. The men were known to be in southeast Missouri when Scherer disappeared.

Former Sheriff Bill Ferrell interviewed both men. In a 2004 interview, he said Lucas told him they kidnapped a female "off I-55 between St. Louis and Memphis."

But when Ferrell showed Lucas a photo of Scherer, who had bright red hair, Lucas said that wasn't the person they kidnapped. He said the victim did not have red hair.

There was no evidence to charge either Lucas or Toole, who both died in prison.

Ferrell said Tuesday he believes Lucas was probably the killer, noting that he said he was in the Scott County area at around the time Scherer went missing, even describing a location where they left a body. Nothing was found there.

"He gave us a lot of information which led us to believe he was probably the one, but we didn't have any way of proving it," Ferrell said.