Editor's note: Some of the details included in the story below may be disturbing for some readers.
Harmony Montgomery's mother, Crystal Sorey, has been wondering for years what really happened to her daughter.
"I knew what he had done to her was for something very small," said Sorey. "Something that a toddler would do."
New documents in the murder case against Harmony's father, Adam Montgomery, have now been unsealed, revealing how prosecutors allege Harmony was killed and what happened after.
"It's been really terrifying," Sorey told NBC10 Boston.
Sorey says she fainted after learning the new details of the case when she met with law enforcement shortly before the documents were released Tuesday morning.
The details about Harmony's final moments come largely from interviews with her step-mother, Kayla Montgomery.
Harmony had been living with her father, as well as Kayla, and the couple's two sons in a car after getting evicted from their Manchester, New Hampshire, home in the fall of 2019.
Kayla Montgomery tells investigators Adam Montgomery was angry with Harmony because she kept having bathroom accidents in the vehicle, and one day in December of 2019, Kayla says Adam hit Harmony three times in the head.
The couple soon realized the child was dead from her injuries.
“They were homeless in that car, and she was too afraid to say that she had to use the bathroom," said a tearful Sorey.
Kayla Montgomery told law enforcement that Harmony's body was placed in a bag and they moved Harmony over the course of the next few months as the family found new places to live, at one point transporting the bag in a stroller.
"The fact he had to move her around from place to place trying to cover his own tracks is despicable to me," said Sorey. "It was his own baby."
Harmony was kept in a cooler in a common hallway of an apartment building, and then a ceiling vent in a family shelter, according to court documents.
When Adam Montgomery got a job at the Portland Pie Company in Manchester, the bag was moved into a cooler at the restaurant, and then finally to a refrigerator and freezer in another Manchester apartment the couple had moved into.
In the spring of 2020, Kayla Montgomery says Adam Montgomery rented a U-Haul and drove for several hours to dump the body someplace, and came back and told her, "it's done."
"I'm hoping that somebody is going to come forward and say, 'Hey, I remember that U-Haul,'" said Sorey.
Harmony's remains have yet to be found.
"There's still hope I'll be able to bring her home," said Sorey.
Read the Harmony Montgomery court documents below:
vere as part of the investigation into Harmony's disappearance. But nothing was found.
Authorities are still asking for the public's help finding Harmony's body or providing information about how she was killed by calling or texting 603-203-6060, the state and local police 24-hour tip line.