The 44-year-old escaped custody while the van was parked at a McDonald's on the North Loop in Conroe.
Conroe Police Department Lt. Dorcy McGinnis said, "Marks escaped on foot and in an eastern direction."
Around 7:30 a.m. Sunday, police were called by the Texas Prisoner Transport Services, to report an inmate had escaped from their transport van.
Investigators say two guards and 10 prisoners were originally in the van when it made the stop.
Marks was being moved from Grand Rapids, Michigan after being captured on a burglar charge by U.S. Marshals.
The transport service was on its way to Bell County where he's wanted in the January murders of two people in Temple, Texas.
"Marks also has warrants for the murders of Michael Swearingen, age 32 and Jenna Scott, age 28," said Lt. McGinnis.
The van started its journey in Michigan, where Marks was picked up. It also made a stop in Louisiana, before passing through Conroe Saturday on its way to Temple.
There is an investigation underway to determine how this happened with the transport company.
Police believe at least one guard was in or near the van when Marks escaped.
Marks was wearing leg, hand and belly restraints during transport. Police are trying to determine how many he was able to remove.
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