"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," said Michael Garrity, a spokesperson for Attorney General John Formella. "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. Montgomery’s total sentence of 43.5 years for these additional charges stands and is not affected by the Court’s decision today." 

According to the ruling, jurors were given strong evidence that Adam Montgomery beat Harmony months before her death, which improperly allowed them to draw the conclusion that he beat her again in December 2019, resulting in her death, in an incident where there was less evidence.

"The State's case on the second degree assault charge was strong," the court's opinion reads. "Three witnesses testified to observing the victim with a black eye in July 2019. Four witnesses, including two who observed the victim's black eye, testified that the defendant admitted striking the victim."

Only one witness linked him to the December assault believed to have resulted in Harmony's death, however. That was Kayla Montgomery, Adam's then-wife and Harmony's stepmother. She was granted a deal with prosecutors in exchange for her testimony, and the defense challenged her credibility.

"We are absolutely disgusted by the decision of the New Hampshire Supreme Court," said the adoptive parents of Harmony's brother, Jamison, Johnathon Miller and Blair Miller. "The reality is — more protection is in place for this monster than Harmony Montgomery ever received."

The murder case was remanded to a lower court, where prosecutors said they are confident they will prevail again.

"We remain confident in the facts of this case, the evidence presented, and the exceptional work of our prosecutors, investigators, and law enforcement partners," Garrity said. "We will continue our efforts to seek justice for Harmony Montgomery and all those who knew and loved her."

Police arrested Montgomery in January 2021 after Harmony's mother, who did not have custody and was no longer involved with Montgomery, reported her missing.

Investigators in Manchester, New Hampshire, discovered the girl had been unaccounted for since 2019.

On Dec. 7, 2019, the day investigators believe Harmony died, she had soiled herself in her sleep, prosecutors said.

Her father allegedly beat her over the head, telling his then-wife Kayla Montgomery, "I think I really hurt her this time."

Harmony was never seen again.

The defense painted Kayla Montgomery as an unreliable witness and attempted to blame her for the crime, arguing during trial that she was the last person to see Harmony.

The court found that trying the murder charge alongside the related counts was unfair to Adam Montgomery as a result — even though his defense had requested the initial joinder. After receiving more evidence, he later tried to have the cases severed, unsuccessfully.

"While the jury heard no evidence that Kayla had ever physically assaulted the victim, it heard evidence from multiple witnesses that the defendant physically assaulted the victim in July 2019," the ruling reads. "Thus, there was a significant risk that the jury would draw the impermissible inference that because the defendant assaulted the victim before by striking her in the head, he must be the one who fatally assaulted her in December by again striking her in the head."