Crime Mass. Teen Is Stabbed 32 Times By Ex After She Started Dating Someone Else: 'He Wanted Her Dead' A month before her murder, Kathryn Mauke broke up with Nikolas Lacrosse By Harriet Sokmensuer Published on May 24, 2018 01:09PM EDT A Massachusetts man was convicted of murdering his teenage ex-girlfriend by stabbing her 32 times after she began dating another person, PEOPLE confirms. Nikolas Lacrosse, 23, was found guilty by a jury Wednesday of first-degree murder in the death of 17-year-old Kathryn Mauke, a Hampded Superior Court official tells PEOPLE. Mauke was discovered dead on her kitchen floor in February 2015. A month before her murder, Mauke broke up with Lacrosse, and by the time she was killed, she had started dating another person, according to MassLive.com. The defense argued that Lacrosse was not criminally responsible for Mauke’s death because he was in a dissociative state when he killed her, MassLive.com reports. “The commonwealth would like you to believe that all of a sudden now he’s this cool calculated guy,” defense attorney Alan J. Black said, “Going over there with a knife to kill her.” Kathryn Mauke/Facebook Black continued: “Is that a reasonable explanation or did he, quote, lose it?” On Friday, Lacrosse testified that he went over to Mauke’s house the day she died for “clarification” on why she broke up with him. Springfield Police Department • Want to keep up with the latest crime coverage? Click here to get breaking crime news, ongoing trial coverage and details of intriguing unsolved cases in the True Crime Newsletter. But prosecutors said Lacrosse stabbed Mauke 32 times with the intent to kill her, MassLive.com reports. “The defendant used a level of severity reserved only for cold-blooded murderers,” Assistant District Attorney Mary Sandstrom told jurors during her closing arguments Tuesday. “He wanted her dead. He wanted to make sure of it.” Sentencing will take place Thursday, according to the outlet. First-degree murder charges carry a mandatory sentence of life in prison without parole, MassLive.come reports. Black could not be reached for comment Thursday so it was unclear if Lacrosse plans to appeal his conviction. Mauke’s family is expected to make victim impact statements during sentencing, according to MassLive.com.