<text>  A Massachusetts teenagers confession to police that he killed his math teacher cannot be used in his murder trial, a judge ruled Tuesday even as he allowed a bloody box cutter and other key pieces of evidence to be admitted. The ruling came in the case of 16-year-old Philip Chism, who has pleaded not guilty to raping and killing 24-year-old Danvers High School teacher Colleen Ritzer on school grounds in October 2013. Chisms lawyers had argued that police coerced their client, then 14, into making detailed statements about the killing, despite invoking his right to remain silent. Prosecutors maintained Chism and his mother had never absolutely demanded a lawyer. Scroll down for video . Confession not admissible: Philip Chism - seen here in a Massachusetts court in January - confessed to police that he killed his math teacher, however a judge has ruled it cannot be used in his murder trial . Essex County District Attorney Jonathan Blodgett, through a spokeswoman, said his office was still reviewing the decision. Calls to Chisms public defenders seeking comment were not immediately returned. Ritzers family said in a statement it respected the court ruling and was confident that law enforcement acted responsibly and lawfully in investigating their daughters killing. The 48-page decision came after days of arguments and testimony on the defenses motion to suppress key pieces of evidence in the case. Salem Superior Court Judge David Lowy concluded that Chism had willingly talked to police in the town of Topsfield on the night of the killing, calmly answering questions and even correcting officers at various points. But Chisms demeanor changed when he was taken to the Danvers police station and further interrogated in his mothers presence, the judge noted. At that point, Lowy said, Chism grew uncomfortable and somewhat hostile. Murdered: Colleen Ritzer was a popular and enthusiastic math teacher at Danvers High School. Phillip Chism has pleaded not guilty to her rape and murder . Charged: Philip D. Chism was indicted by an Essex County grand jury today on charges of first-degree murder, aggravated rape and armed robbery in 2013 . He twice indicated his disinterest in speaking with Danvers police and did not appear to be fully engaged or to appreciate the seriousness of what officers asked him as they explained his Miranda rights, the judge wrote. It is clear that the defendant wanted to talk to the police without his mother present in the room, Lowy said in his ruling. It is also clear that he had no intention of talking while his mother was in the room. As a result, the judge said, he would allow the statements Chism made to Topsfield police to be introduced as evidence but not his taped confession at the Danvers police station. He also allowed items gathered at Danvers High School, as well as those seized from Chisms pockets and backpack. They included Ritzers ID and credit cards, a bloody box cutter and womens underwear. In memoriam: The campus of Danvers High School was flooded with flowers and other tokens following the October 2013 murder of teacher Colleen Ritzer . R.I.P.: Danvers High School community mourns the tragic death of beloved math teacher Colleen Ritzer whose body was found behind the school . But Lowy ruled prosecutors cannot use evidence from Chisms and Ritzers cellphones, which were found near a movie complex. Authorities say surveillance video from October 22, 2013, shows Chism following Ritzer into a school bathroom, wearing gloves and a hood, then later walking out of the bathroom alone. A short time later, the video shows Chism pulling a recycling barrel through the school and outside. Ritzers body was later found in nearby woods, naked from the waist down and with her throat slit and a note that read, I hate you all. Authorities said she was sexually assaulted with a stick. A bloody recycling bin was found nearby. Dianna Chism left attends her son Philip Chisms hearing in Suffolk County Juvenile Court Wednesday, July 23, 2013, in Boston, where he was arraigned for allegedly assaulting a state worker while he was in custody at a Department of Youth Services facility . Chism, who had recently moved to Massachusetts from Clarksville, Tennessee, was found that night by Topsfield police walking along a nearby highway. Prosecutors allege that after the killing, Chism used Ritzers credit card to buy fast food and attend a movie at the mall. Chisms trial is scheduled for October 7. Both sides are expected back in court for a pre-trial hearing on April 9. 