FARGO, N.D. -- The father of a Wisconsin teenager accused of killing his sister in Fargo, N.D., said the judge in the case should have accepted a plea agreement.

Sergei Carlson, 16, of Sun Prairie, is charged with murder and a deviate sexual act in the death of his sister, Whitney Carlson, 16.

In a letter to Judge John Irby, the Rev. Scott Carlson said the judge's rejection of a plea deal in May made him feel like he had been kicked in the stomach.

He said he'd hoped his son could serve a 30-year sentence and be rehabilitated after Carlson allegedly murdered his 16-year-old sister Whitney, WISC-TV reported.

The plea agreement called for a sentence of 30 years in prison for the teen.

But defense attorney Mark Beauchene said in court documents that Irby would only accept a sentence of life in prison with the possibility of parole.

Beauchene had asked Irby to remove himself, alleging the judge was biased against Sergei Carlson. He also asked that the trial be moved from Fargo.

On Wednesday, the judge agreed to move the trial from Fargo, but Irby refused to remove himself from the case.

Sergei Carlson was adopted from Russia when he was 7 years old and moved with his father to Sun Prairie, Wis., in 2002. Whitney Carlson lived with her mother in Fargo.