The bodies of 8-year-old Hannah Marshall and Makayla Roberts, 10, were found in a car on Frederick Blair's marijuana farm, in Norwood, Colorado, in 2017
Credit: San Miguel County Sheriff's Office

A member of a Colorado group with “apocalyptic” beliefs has accepted a plea deal in connection with the deaths of two girls that group members are accused of intentionally abusing until they died, PEOPLE confirms.

The children — 8-year-old Hannah Marshall and 10-year-old Makayla Roberts — were found mummified in a car on Frederick “Alec” Blair’s marijuana farm in 2017.

Hannah and Makayla were forced to live inside the vehicle without food or water and were victims of the religious beliefs of the small group, which included their mom, investigators have alleged, according to the Grand Junction Daily Sentinel.

“It was an apocalyptic kind of thing,” a source with knowledge of the case previously told PEOPLE of the group.

“They are guided by their dreams,” the source said, describing the group’s beliefs. “They will stay some place until they have a dream and then they go someplace else. They think they can heal people.”

Blair was originally charged with being an accessory to a crime and two counts of child abuse resulting in the deaths of both girls. Their remains were discovered in the backseat of the car on Blair’s farm near Norwood, about 30 miles west of Telluride, on Sept. 8.

Due to extreme decomposition, it is unclear how Hannah and Makayla died — whether from dehydration, heat or starvation.

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Under his plea agreement last week, Blair admitted being an accessory, a class-four felony, and the child abuse charges against him were dropped. Prosecutors say he has agreed to cooperate against the remaining suspects in the case.

Blair is scheduled to be sentenced on Sept. 27 and faces up to 12 years in prison, a prosecutor’s spokesperson says. He remains in custody in lieu of $125,000 bond.

Speaking with PEOPLE, his attorney, Kristen Hindman, described how Blair “changed profoundly” under the “coercive” influence of the group, transforming from “a very congenial sort of happy person who would really give the shirt off his back to anyone to someone who completely cut off all ties to his family and friends and the community.”

“He burned his possessions. He tried to kill his most beloved possession, which was his dog, at the direction of the [group’s] leaders and it ultimately led to this tragedy where he rendered assistance in covering up the deaths of these children,” Hindman said.

Also charged in connection with the case were Madani Ceus, the group’s alleged leader; Nashika Bramble, the mother of the two girls; Ashford Nathaniel Archer, Ceus’ partner; and Ika Eden, another group member.

Bramble and Ceus are charged with two counts of first-degree murder and two counts of child abuse resulting in death. Archer and Eden each face two counts of child abuse resulting in death, and Archer is also charged with one count of being an accessory to a crime.

All four are slated to go to trial by December and have pleaded not guilty. None of their attorneys could be reached for comment by PEOPLE this week.

From left: Frederick Blair and Madani Ceus
| Credit: San Miguel Sheriff's Office

‘A Reign of Terror’

Before Hannah and Makayla died, they lived as two of the youngest members of an itinerant group led by Archer and Ceus who, over the course of two years, moved across dozens of states before landing in Colorado.

Archer and Ceus remain mysterious figures, including how they met, though they reportedly began gaining followers in 2015.

This account of the group’s activities and the specific events before the two girls died is according to a lengthy series published by the Daily Sentinel in January. For its reporting the paper cited court testimony and court documents among other sources.

(Prosecutors declined to comment to PEOPLE on the newspaper’s account and local investigators did not return messages seeking comment.)

Authorities reportedly said Ceus, Bramble, Archer and Eden were staying in Grand Junction before relocating to Norwood. There they met Blair at a gas station in May 2017 and began living in their cars, makeshift huts and tents on Blair’s farm.

Ashford Archer
| Credit: San Miguel Sheriff's Office

The group believed last year’s solar eclipse in the U.S. would mark the apocalypse, bringing days of darkness, during which time they would be transported to another dimension via a “light body,” San Miguel County Sheriff Bill Masters alleged in January.

According to the Daily Sentinel, Blair was interviewed by authorities and gave a detailed description of events the summer before Hannah and Makayla’s deaths.

Ceus — having, one defense attorney claimed, “engaged in a reign of terror” and threatened others with “abomination” after a member of the group was exiled — allegedly declared that Makayla was a danger to the group and was a “harlot” in a previous life, Masters said.

“It started with identifying Makayla as being evil,” he testified at a January hearing. “So the first step was she was not allowed to play with the other children.”

Makayla was allegedly made to live in a Toyota Camry on the property so she that wouldn’t purportedly infect the group, Masters said. In late July, she was eventually refused food and water because Ceus considered the food sacred.

As Makayla was kept captive, Masters said, Blair was “shocked” to learn that another girl whom he had never seen had been living in the Camry since they moved onto his property: It was Hannah, Makayla’s little sister and Bramble’s other daughter.

Nashika Bramble (left) and Ika Eden
| Credit: San Miguel Sheriff's Office

Leader Described Victims as ‘The Death of Us All’

The group allegedly deprived both girls of food and water, Masters said, and prepared for the solar eclipse on Aug. 21. Members were forbidden to interact with the car or with the children inside, though the vehicle was still unlocked.

“Ms. Ceus said, ‘These girls will be the death of us all,’ ” Masters testified.

Blair told police that in mid-August, Bramble went to check on her daughters and discovered they were dead, after which Ceus allegedly instructed some of the group’s members to “cover the car with a tarp,” according to a sheriff’s deputy’s testimony. The vehicle’s doors were also taped shut.

On Aug. 21, when the foretold apocalypse did not occur along with the eclipse, Ceus allegedly blamed “other family members for not being pure enough,” Masters said.

She is further accused of ordering both Blair’s dog and then Bramble to be denied food and water.

“Ms. Ceus confronted Bramble stating that she had been an evil person in her past life and that she hadn’t done enough to try to get rid of all this evilness that she was carrying around with her,” Masters testified.

Allegedly banished to a vehicle, Bramble soon fled Blair’s farm back to Grand Junction, according to authorities.

“According to Blair, Nashika sees the writing on the wall, if you will, and believes that she’s going to be the next person sent to abomination,” Masters said.

Blair’s stepfather previously told PEOPLE that in late August or early September, the family got a call from a friend of Blair’s who had stopped by his property and saw that Blair’s dog was malnourished.

Blair’s father, alerted by his mother, drove from Texas to his son’s farm where he called law enforcement.

Authorities subsequently discovered the girls’ bodies still in the Camry — with a diary nearby, whose contents have reportedly not been made public — and then arrested Ceus, Archer, Blair and Eden on Sept. 8. Bramble turned herself in in Grand Junction the next day.

“They were the most sweetest, genuine loving girls, always hugging me, always just giving me affection,” one former member of the group told the Daily Sentinel of Hannah and Makayla. “Those girls did not deserve it.”