WEST PLAINS, Mo. -- A Doniphan, Mo., teenager preempted his trial this week by pleading guilty to sexually assaulting an elderly woman.

Christopher Aaron Casteel's trial was supposed to begin Wednesday and continue through Friday in Howell County on the unclassified felony of forcible rape, the Daily American Republic newspaper reported. The 18-year-old was accused of raping an 89-year-old woman, who was staying at a rural Doniphan home, on Nov. 6.

"We had to plead that down; the victim was too frail to make a good identification," explained Ripley County Prosecuting Attorney Christopher Miller. " ... She's not 90 yet, (but) very close and in very, very poor health."

Miller filed an amended information with the court Monday, charging Casteel with the Class C felony of sexual assault.

It alleges on Nov. 6, Casteel "had sexual intercourse with (the victim) knowing that he did so without" her consent.

Casteel, Miller said, pleaded guilty to the amended charge and waived having a sentencing assessment report completed by Probation and Parole.

Presiding Circuit Judge David Evans followed the plea negotiations in sentencing Casteel to three years in the Missouri Department of Corrections, Miller said. "He'll have to register as a sexual offender when he gets out," he said.

Obviously, Miller said, the victim's family would have liked Casteel to get more time, but "they were seriously concerned that the continuation (to trial) would adversely affect their mother."

The stress, Miller said, was more than the woman's family wanted her to have to go through. "I understand that; she was very, very ill," he said.

After Monday's court appearance, Miller said, Casteel was transferred back to Ripley County, where he has two Class C felonies second-degree burglary and two Class C felonies of second-degree arson pending.

"This was a negotiated plea; we negotiated a three-year sentence on the sexual crime with no limits on the burglary and arson cases," Miller said. "His plea was not contingent upon what he gets in the arson(/burglary) case."

Casteel, Miller said, could get up to 28 years in prison should he receive the maximum of seven years on each charge and the sentences are ordered to run consecutively.

Miller said he and Casteel's public defender have no plea agreement as to the burglary/arson case.

"If we don't work something out on that; we'll try him here (Ripley County) on those cases," Miller said.

Casteel, along with Jonathan A. Hart, are accused of burglarizing two buildings on County Road 142E-8 in rural Ripley County, as well as damaging a barn/shed, motor vehicle and a trailer house by fire in March.

At about 3:45 p.m. March 28, Hart "admitted to setting fire to a barn/shed and a motor vehicle, causing the barn/shed and the motor vehicle to be destroyed by fire," Missouri State Highway Patrol Sgt. Dennis Overbey said in his probable cause statement.

Casteel, Overbey said, allegedly was with Hart when "he set the barn/shed and motor vehicle on fire."

The barn/shed and motor vehicle were owned by Linda Campbell Holt, while the trailer house was owned by Steve Collins and Larry Carter.

Casteel is to appear at 9 a.m. Sept. 20 before Presiding Circuit Judge Robert Smith for a motion hearing in his case.

A pretrial conference is set for 9 a.m. Oct. 4, with the jury trial scheduled for 8 a.m. Nov. 5.