Barbara Lenz, 31, was last seen on May 6, 1989. After 36 years later, her former boyfriend Robert Davis, 61, was arrested and charged with first-degree murder in her disappearance.

Robert Davis was the last person to see his girlfriend Barbara Lenz alive before she vanished in 1989, Iowa investigators said.

The woman’s body has not been found, but investigators believe the now 61-year-old man had a “motive to kill” his girlfriend.

His arrest is the result of an investigation by the state's cold case unit, launched last summer by Iowa Attorney General Brenna Bird's office to investigate the state's more than 400 unsolved murders.