JEFFERSON CITY, Mo. -- Two convicted murderers missing from a state prison carefully planned their disappearance -- stocking up on food and clearing out their cells before killing a fellow inmate and fleeing, law officers said Friday.

The missing items provided the most concrete evidence yet that inmates Christopher Sims and Shannon Phillips killed fellow convicted murder Toby Viles Wednesday evening as part of an elaborate plan that authorities are still trying to piece together.

"This was not a crime of instant passion," Cole County Sheriff John Hemeyer said Friday. "Whatever happened to this point was something that they were anticipating and planning on."

Despite the efforts of 200 searchers now in their third sweep of the 47-acre Missouri State Penitentiary, there still was no evidence Friday that the two inmates either successfully escaped or were still hiding within the walls, said Department of Corrections spokesman Tim Kniest. Neither were there any confirmed sightings of the men outside the prison.

"We've got even odds -- inside, outside -- at this point," Hemeyer said. But he acknowledged that the likelihood of a successful escape increases with each passing hour.

A note left beside Viles' body and initialed by the missing inmates claimed his murder and threatened to kill anyone who attempted to confront them, Hemeyer has said. Viles was killed in a prison ice plant, where all three had been working without direct supervision.

Preliminary autopsy results released Friday indicated Viles died of blunt trauma to the head, Kniest said.

Gone from the missing inmates' cells were their bed sheets, blankets and any valuable items, Hemeyer said.

The two prisoners also emptied out their inmate bank accounts, purchasing packaged meats, candy bars and food items from the prison store, he said.

All of those items could have been used or taken with them in an escape, or they could have been traded as black-market currency to pay off people or obtain other supplies, Hemeyer said. It's also possible that the inmates, normally dressed in gray garb, had access to civilian clothes or Corrections Department uniforms, the sheriff said.

"The guys had plenty of time to plan, and it looks like from what I have been given it was very well planned," said Capt. Ray Bledsoe, a spokesman for the Jefferson City Police Department.

After a day of high alert Thursday, with door-to-door questioning and police checkpoints around the capital city, Bledsoe said police had returned Friday to a routine work schedule because of a lack of leads.

Prisoners also were under somewhat relaxed lock-down procedures -- still barred from leaving their cells for work, educational classes or recreation, but allowed to leave for showers and visitations. They were scheduled to eat in the dining hall Friday evening, Kniest said.

Prison officials last had contact with Viles during a telephone call to the ice plant about 6:10 p.m. Wednesday. His body was not discovered until about 10 p.m., giving the other two inmates nearly four hours to flee.

Kniest said there were no employee shift changes during that time and it was unlikely that any vehicles entered or left the prison. But he said many prisoners were free to walk around at the time while going to eat, work, study or their recreation.

"We do believe that there was a planned escape," Kniest said. But "we're still optimistic that we're going to find the inmates or some evidence that they are not here."

Sims, 27, is serving a life prison sentence for first-degree murder for the 1997 shooting of Gale Brown in north St. Louis. Phillips, 35, is serving a life sentence for first-degree murder for the 1995 stabbing and slashing of Charles Brown in Kansas City.

Viles also had been serving a life sentence for the 1992 first-degree murders of his three siblings -- Tabitha Viles, 14, Quincy Viles, 11, and Tristan Viles, 3 -- at their Laclede County home. Viles was 16 years old at the time of the shootings.