Thomas Lawton Evans, 37, pleaded guilty on Tuesday to kidnapping, transportation of a minor to engage in sexual activity and aggravated sexual abuse in federal court in Charleston, South Carolina.
He faces 30 years to life in prison at sentencing. A sentencing date has not yet been set.
A twist came in court when prosecutors said Evans acknowledged killing his 39-year-old girlfriend, Sharon Nannette Hayden, days before the kidnapping.
Evans told FBI agents he stabbed Hayden in a fight in her Spartanburg County home, prosecutors said.

Her body has never been recovered and Evans hasn’t been charged in her death.
Spartanburg County deputies referred all questions to the FBI. Supervisory Special Agent Donald Wood said his agency does not discuss its investigations.
Hayden’s car was found at the Johns Island home near Charleston where the child’s kidnapping took place, authorities said.
Prosecutors said Evans chose his next victims at random, following a mother and her four-year-old daughter back to their home near Charleston on February 13 and beating the mother so severely she had to be hospitalized for facial fractures.

Evans, meanwhile, drove west with the girl. Railroad workers called police after finding them sleeping in a car in Riverside, Alabama, and Evans handed an officer the girl then sped off, according to authorities.
He was arrested later after a police chase in Mississippi, authorities said.
Evans still faces several state charges, including attempted murder, for the attack on the mother and daughter.
He was arrested in 2000 and charged with second-degree criminal sexual conduct with a minor. Police said he assaulted a 15-year-old girl when he was 19. At the time he wasn’t required to register as a sex offender because he pled guilty to a lesser charge.
In 2002, Evans was accused of robbery when he and another man grabbed a woman in downtown Charleston and attempted to snatch her purse. He was convicted of strong armed robbery and served two years probation.