Authorities combed an area southwest of the Montana State Prison on Sunday for two escaped inmates, including one once accused of plotting to kidnap David Letterman's son, who escaped while working at the prison's ranch.

Kelly A. Frank, 45, and convicted burglar William J. Willcutt, 22, were assigned to a crew that moves irrigation pipe at the ranch, prison officials said.

A supervisor noticed Willcutt and a truck were missing Friday afternoon, a prison statement said. The prison was locked down and an inmate count showed Frank was also gone.

The truck was later found off prison property near Deer Lodge, in western Montana.

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Department of Corrections spokesman Bob Anez would not say where the truck was found, but he said ground crews and the crew of a Highway Patrol helicopter focused their search Saturday on an area between Deer Lodge and Anaconda. Crews planned to search through the night.

Frank was arrested in March 2005 on allegations that he had devised a plan to kidnap Letterman's son, lied to investigators and overcharged Letterman for painting work at his ranch.

Prosecutors later dropped a charge of solicitation to kidnap, in exchange for guilty pleas on three other charges, including felony theft and misdemeanor obstruction.

Frank was sentenced to 10 years in prison for overcharging the talk show host.

There was no immediate response to calls and e-mails seeking comment from Kim Krizzo-Emmet, Letterman's publicist at CBS.

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