AP

This image provided by the Illinois Department of Corrections shows Robert B. Rhoades, a trucker who kept a torture dungeon in the cab of his long-haul rig.

A serial killer who set up a torture chamber in his truck and kidnapped mostly female hitchhikers across the United States has admitted murdering a newlywed couple in Texas, according to reports.

Robert Ben Rhoades -- already serving a life sentence for the death of a 14-year-old girl in Illinois -- this week pleaded guilty in West Texas to killing Patricia Candace Walsh and her husband Scott Zyskowski, both in their 20s, the Deseret News reported.

Prosecutors had agreed not to seek the death penalty in exchange for the pleas and Rhoades, 65, was given two life sentences, the News said.

The paper said Rhoades, a long-haul truck driver, was the subject of the book "Roadside Prey" by Alva Busch.

In his cab was "a type of dungeon with handcuffs on the ceiling," the News reported. In 1996, the Tucson Weekly, citing officials, said it was believed that Rhoades had been killing an average of three women a month by the early 1990s.

The Associated Press reported the couple, from Seattle, were hitchhiking to Georgia to preach the Christian gospel, when they took a ride from Rhoades near El Paso, Texas in early 1990.

FBI spokeswoman Shauna Dunlap said investigations concerning Rhoades were continuing.

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