The New Hampshire Supreme Court has overturned the murder conviction of a man who was accused of killing his 5-year-old daughter in 2019, ruling June 11 that he did not receive a fair trial because key charges were improperly combined.Adam Montgomery, 36, was found guilty in February 2024 of second-degree murder in connection with the death of his daughter, Harmony Montgomery, whose body has never been recovered, USA TODAY previously reported. He was also convicted of second-degree assault, abuse of a corpse, falsifying physical evidence and witness tampering.Montgomery was sentenced in May 2024 to 56 years to life in prison, including a 45-year to life term for the second-degree murder conviction. Additional time was imposed consecutively for the other convictions.In a decision issued June 11, the New Hampshire Supreme Court reversed the second-degree murder conviction, arguing that the murder and assault charges should not have been prosecuted together. The court upheld the other convictions but remanded the second-degree murder charge to a lower court for further proceedings."We conclude that, under these circumstances, trying the second degree assault and second degree murder charges in a single trial jeopardized the defendant’s right to a fair trial," the court wrote in the 15-page ruling.Despite the ruling, Montgomery will not be released from prison as his other convictions still stand. He will continue to serve his sentence on those charges, as well as a separate 32½‑year sentence he was already serving on unrelated gun charges.“We are disappointed by the Court's decision to order a new trial on the second degree murder charge and we plan to pursue a re-trial on that charge," the New Hampshire Department of Justice said in a statement to USA TODAY. "Adam Montgomery remains convicted of multiple serious felonies arising from Harmony's death, as well as separate firearms offenses that were previously upheld on appeal."USA TODAY has reached out to Montgomery's attorney’s office for comment.Harmony Montgomery was not reported missing for almost 2 yearsAuthorities believe Harmony was killed in Manchester, a city less than 20 miles south of the New Hampshire capital of Concord. The girl was last seen in 2019 but was not reported missing until late 2021, according to authorities.The New Hampshire Department of Justice previously reported that Harmony was last seen after being evicted with her family from a Manchester home the day before Thanksgiving. Investigators later determined that she was with her father and stepmother in the days following the eviction, as the family lived out of vehicles and moved around the city.Authorities said the circumstances made it difficult to trace the girl’s movements, but multiple witness accounts helped narrow the timeline of her disappearance. Witnesses told police they saw Harmony with the couple in the days after Nov. 27, 2019. But by early December 2019, authorities said, the child was no longer with them.At the time, authorities said the investigation had "narrowed the window of Harmony's disappearance to approximately November 28–December 10, 2019." Months later, after an extensive investigation involving local, state and federal agencies, authorities concluded that Harmony had been killed in Manchester in early December 2019.Her body has never been found, but investigators said biological evidence and other findings led them to determine she was murdered, according to the New Hampshire Department of Justice.Adam Montgomery accused of abusing his daughterThe Manchester Police Department arrested Montgomery in January 2022 in connection with his daughter's disappearance and he was later charged in her death.Montgomery, who previously professed his innocence in court, did not attend his trial and was not present when jurors returned their verdict in 2024, USA TODAY previously reported.During the trial, prosecutors alleged that Montgomery beat his daughter to death, put her remains in bags and disposed of them, and abused his wife and pressured her to lie for him in court. At the time, prosecutors said Montgomery would not reveal where he hid Harmony's body."Harmony was an innocent 5-year-old," Hillsborough County Superior Court Judge Amy Messer told Montgomery during his sentencing hearing in May 2024. "You treated her in the worst of possible ways, in both her life and her death."Contributing: Natalie Neysa Alund, USA TODAY; Rin Velasco, USA TODAY Network - New England