FARGO - The lawyer for a teenager accused of killing his 16-year-old sister is asking a judge to throw out the teen's statement to law enforcement officers three days after her death.

Sergei Carlson pleaded not guilty Wednesday in the July 13 killing of Whitney Carlson, of Fargo.

Defense attorney Mark Beauchene filed a motion after the arraignment to suppress evidence from a police interview with Sergei Carlson on July 16. The motion said the interrogation violated Carlson's right to an attorney.

Assistant Cass County State's Attorney Reid Brady said prosecutors would contest the motion. He had no further comment.

Sergei Carlson's trial set for Feb. 5 in East Central District Court. He is charged with murder and a deviate sexual act. He pleaded not guilty to the sex charge earlier. The case has been transferred to adult court.

Sergei Carlson was adopted from Russia when he was 7 years old. He moved with his father, the Rev. Scott Carlson, to Wisconsin in 2002. Whitney Carlson lived with her mother in Fargo.

Authorities said Sergei Carlson told police he strangled Whitney Carlson with his hands, put pillows over her head and had sexual contact with her on the night of July 13.

The motion filed Wednesday by Beauchene said Sergei Carlson believed he was in custody when he was interviewed by police on July 16. Carlson was not provided an attorney, nor was he represented by a parent or guardian, the motion said.

The defense attorney said Carlson was first interviewed by police on July 14. Carlson's father told police two days later that his son could have been responsible for his sister's death, leading to a second interview, the defense motion said.

Carlson's father said he was worried about the defendant's "obsessive behavior" that had been described as an "addictive personality," Beauchene wrote. The father told police he did not want the evidence to point to Sergei Carlson, but said "there's too much at stake," the defense attorney said.

The father was present when authorities read Sergei his rights but left during the interview, Beauchene said.

Police asked Carlson if he wanted his father to leave the room, and Carlson said "sure," Beauchene wrote. After his father left, Sergei should have been represented by a lawyer during the interrogation, the defense attorney said.

Beauchene filed a second motion that would limit prosecutors' use of evidence obtained by a mental health examination of Carlson.

Carlson waived his right to a preliminary hearing at Wednesday's arraignment.

Mark Bourdon, a spokesman for the Carlson family, said he was hoping for a guilty plea and said he doesn't want to see the case go to trial.

"It's heart-wrenching," Bourdon said. "We were hoping that Sergei would take responsibility for actions we believe he took."