There hasn't been a trace of them in more than two weeks.
Authorities, volunteers and relatives have driven up and down roads covering thousands of square miles of Ohio, Kentucky and Indiana and flown over the region. They've looked for credit card activity, studied store videotapes, checked under bridges and passed out thousands of fliers.
Warren County Sheriff's Maj. John Newsom said it is one of the broadest investigations ever in this area about midway between Dayton and Cincinnati.
He said there has been no indication of foul play.
"They're out there somewhere. It may be the next square mile we search," said Brad Nixon, Walters' son-in-law. "The optimism is reduced ... but how do you stop?"
Walter, 68, and Wasson, 80, are believed to have left the closely knit Otterbein Retirement Living Community here on April 19, headed to a J.C. Penney outlet store in either Columbus or Carrollton, Ky., with Wasson driving her 2000 Chevrolet Impala. They were reported missing three days later, when Walters' daughter came to pick her up for an evening out and found worried neighbors.
"That's all we think about," said Dorothy Pfeiffer, Walters' next-door neighbor.
Walters is a mother of three whose husband was in Florida with his own ailing mother, and Wasson is a widow with no children.