“We are going to hold the State of New Hampshire accountable for Harmony’s senseless and preventable death, shine a light on the systemic failures in her case to prevent future tragedies, give Harmony the voice that she never had, and get Harmony the justice that she so deeply deserves,” said Cyrus F. Rilee, an attorney representing Sorey in the case.

Authorities in both New Hampshire and Massachusetts largely overlooked Harmony’s two-year disappearance, and the case has illuminated gaps in child protective services in both states.

“We will review the complaint and respond as appropriate,” said Michael S. Garrity, a spokesperson for the attorney general’s office.

“I’m Harmony’s voice, and I’m her warrior. Everything I do is for her. I can’t let people forget,” Sorey told reporters in March, after a court appearance that paved the way for civil litigation.

According to the lawsuit, Harmony Montgomery lived with her mother in Massachusetts from the time she was born in 2014 until February 2019, when the Massachusetts Department of Children and Families removed the child from Sorey over allegations of neglect. Sorey has said she was struggling with substance abuse at the time.

State officials in Massachusetts worked with New Hampshire’s Division of Children, Youth, and Families, placing the child in her father’s custody in Manchester, N.H., according to the complaint.

It details how about five months after the placement, multiple people, including Adam’s uncle Kevin Montgomery, started making reports to DCYF, expressing their concern about Harmony’s living conditions and her well-being, after she was seen with a black eye.

“Kevin reported that Adam told him he had ‘bounced her off every f—ing wall in this place,’” the lawsuit said. While speaking with a DCYF staffer, the lawsuit said, Kevin Montgomery grew frustrated when he was questioned on the accuracy of his dates, and said “this is why children die” and that “this child was punched clear in the eye socket with full force.”

Another person who reported issues to DCYF also had concerns that Harmony’s situation could end up being fatal for her.

The reports to DCYF included details about unsafe living conditions, how electricity and hot water in the home had been turned off, the presence of drug paraphernalia, and how Harmony’s father punished her by forcing her to stand in the corner for hours or stay in her bedroom from when she woke up until the late afternoon, according to the lawsuit.

Reports were also made to DCYF about how Harmony wasn’t receiving care from a doctor, and that in the fall, she hadn’t been enrolled in school, according to the lawsuit.

The lawsuit argues that the state was negligent and didn’t meet minimum standards of care for Harmony, even after receiving reports about physical and emotional abuse and neglect by her caretakers.

It also says that the state failed to launch a thorough and competent investigation into reports of suspected abuse, exposing Harmony to “foreseeable harm.” According to the lawsuit, as a direct result of DCYF’s negligence Harmony endured corporal punishment, verbal and mental abuse, and beatings that ultimately caused her death.

Sorey has said she didn’t hear from the girl’s father after 2019, and she grew frantic in 2021. At that point, she turned to the Manchester police and mayor’s office, resulting in an investigation that culminated in Adam Montgomery’s arrest.

New Hampshire Governor Chris Sununu slammed the Massachusetts courts for placing Harmony with a “monstrous drug dealer.” But this lawsuit contends that child welfare workers in New Hampshire were ultimately responsible because they didn’t remove her from his custody after receiving reports of his abuse.

Sununu’s office released a seven-page report in February 2022 acknowledging that a New Hampshire child welfare worker repeatedly made contact with Adam Montgomery after his daughter’s disappearance. At least twice, the worker asked specifically about Harmony’s whereabouts, and Adam Montgomery claimed he had returned the girl to her mother. The worker left a voicemail for Sorey in January 2020, but the message went unreturned, and there is no evidence that any additional attempts were made to contact her, according to the report.

The Massachusetts Office of the Child Advocate released a 100-page report in May 2022, acknowledging that the state’s child welfare system overlooked Harmony’s needs at every turn.

Material from prior Globe reports was used in this article.

Amanda Gokee can be reached at amanda.gokee@globe.com. Follow her @amanda_gokee.