A former small-town police chief and convicted murderer who escaped from a prison in Calico Rock Ark., on May 25 apparently used his job in the prison’s kitchen to help plan and carry out his escape, according to prison officials.

They believe that the prisoner, Grant Hardin, took advantage of his kitchen assignment to study staff movements, access restricted areas and gather materials for a disguise that helped him slip past security, Rand Champion, a spokesman for the Arkansas Department of Corrections, said in an interview. Mr. Hardin, 56, was captured on June 6; he pleaded not guilty to second-degree escape on Tuesday.

Mr. Hardin spent months preparing, the authorities believe, watching the prison’s routines from inside before picking the right moment to make his move.

“This wasn’t something he came up with that Sunday morning when he woke up,” Mr. Champion said. “This was well thought out and was something he had been planning for a while.”

Officials have started to interview Mr. Hardin, but they say that won’t know for sure how he pulled off his escape until they finish speaking with him — or at least examine the altered uniform. Still, early evidence — including prison video and an examination of kitchen utensils and food — suggests he had used his kitchen job to help him alter one of his old white prison uniforms.

The prison kitchen is stocked with tea, coffee, spices and markers used for labeling, Mr. Champion said. Mr. Hardin may have dyed an old prison uniform with tea, darkened it with coffee, used ink from a permanent marker — or, possibly, all three, Mr. Champion said.