A Missouri judge has blocked prosecutors from using part of a teenager's statement to police in her upcoming murder trial for the slaying of a 9-year-old neighbor girl.

In a decision released Wednesday, Cole County Circuit Judge Patricia Joyce said a juvenile officer wrongly participated in a state Highway Patrol interview of Alyssa Bustamante and "used deceptive tactics" while the teenager was being questioned about the death of Elizabeth Olten in October 2009.

Bustamante, who was 15 at the time of Elizabeth's death, has pleaded not guilty to an adult charge of first-degree murder. Her trial is scheduled for Sept. 13.

At a November 2009 hearing in which Bustamante was certified to stand trial as an adult, Missouri State Highway Patrol Sgt. David Rice testified that she had confessed to the slaying and led authorities to Elizabeth's well-concealed body in the woods near where the two girls lived just a few houses apart in the Jefferson City suburb of St. Martins. Rice testified that Bustamante "stated she wanted to know what it felt like" to kill someone.

It was unclear from the court order released Wednesday whether that particular statement would be inadmissible during Bustamante's trial. The judge's suppression ruling referenced a page and line number on a transcript of Bustamante's videotaped statement, which has not been publicly released. The defense motion to suppress the statement had been filed under seal.

Assistant prosecutor Anji Gandhi and Bustamante's attorney, Charles Moreland, both said separately that they were prohibited from detailing whether the judge's order suppressed the statements referenced in court in 2009, or even whether the order covered most or only a small portion of Bustamante's statement.

But "what may have been heard at the juvenile hearing is not going to be relevant for what's heard at this trial," Moreland said. "When this thing is tried, the jury is going to hear a very different case than what was heard at that juvenile hearing."

Gandhi declined to comment on the affect the judge's order would have on the prosecution's case.

Because Bustamante was in juvenile custody at the time of her statement, anything she said to juvenile officer Tobie Meyer is inadmissible in her adult criminal proceeding, the judge said. The court order initially released Wednesday said Bustamante's statements to patrol officer Rice could have been used in an adult court trial had Meyer not participated in the questioning. But that assertion was deleted in what the court described as a corrected order released later Wednesday. Both orders were dated Tuesday and signed by Joyce.

"Ms. Meyer used deceptive tactics during the interrogation of defendant by telling defendant that she was there as the defendant's 'advocate,'" Joyce wrote while noting the juvenile officer's role should have been limited to observation and protection of Bustamante's rights.

"This deception likely mislead the defendant into believing that Ms. Meyer was there to look after her best interests when she encouraged defendant repeatedly to tell the truth," Joyce said in originally released court order. The revised version struck the reference to repeatedly encouraging Bustamante to tell the truth.

The administrator of the Cole County juvenile office did not immediately respond to a message left Wednesday by The Associated Press.

At the November 2009 hearing, authorities also had testified that Bustamante dug two holes in the ground to be used as a grave, then attended school for about a week while waiting for the right time to commit a murder. Law officers said Elizabeth had been at Bustamante's home on the day in which she was strangled, cut and stabbed with a knife.

Hundreds of volunteers participated in a two-day search for Elizabeth before her body was found.