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(CNN) -- A mentally disabled woman and her daughter were held in an Ohio apartment crowded with people and animals for more than a year, forced to perform manual labor and threatened with dogs and snakes to keep them compliant, authorities said Tuesday.

Federal prosecutors said the people accused of holding the pair in Ashland, about 60 miles south of Cleveland, collected the woman's government benefits and beat her in order to get painkillers for themselves. They kept her in a room with a free-ranging iguana and ordered her to feed the reptile fruits and vegetables her daughter was denied, according to court papers. Sometimes their captors' pit bulls got table food while they had to eat from cans, according to an arrest affidavit quoting witnesses.

"The living conditions were simply subhuman," said Steven Dettelbach, U.S. attorney for the Northern District of Ohio.

"(We're) talking about people who were locked in rooms, forced to work all the time, people who were threatened and beaten and injured, people who were exploited, people who had their money and benefits stolen, sort of used as pawns to get drugs," he told CNN's Erin Burnett. "And the worst part of all this is, you know, they tried to rob the victims of their basic human dignity. So almost everything they did was to prey on them, prey on their vulnerabilities and exploit them."

The mother and daughter were sometimes forced to eat dog food, according to a law enforcement source with firsthand knowledge of the investigation.

They were also frequently denied access to the bathroom, FBI Special Agent Eric Smith told reporters.

"They were physically punished for toiletry accidents," he said, "and they were threatened not only with weapons but also with vicious animals, to include pit bulls and pythons."

Family and attorney deny accusations

Three people -- 26-year-old Jordie Callahan, 31-year-old Jessica Hunt and 33-year-old Daniel Brown -- were arrested and charged with forced labor. Callahan is facing an additional count of witness tampering, and another arrest could come soon, the U.S. attorney's office in Cleveland said.

Callahan's mother, Becky, told CNN's Piers Morgan that the accusations are false, and that the alleged victim was allowed to leave the apartment whenever she wanted.

"There are so many lies going on," she said, accusing investigators of trumping up the case to draw attention to the small city of Ashland.

"She was giving them a couple hundred dollars a month for staying there. She was getting her own food. She wasn't being starved," Callahan's mother said.

Her son, she said, is devastated by the accusations.

"He's devastated that all of this is being said about them. They have some pit bulls and snakes, so they are making them out to be evil because they have that," she said. "He loves reptiles. He always has since he was a kid."

An attorney for Callahan told CNN affiliate WOIO that the allegations are ludicrous.

"She had opportunities to leave. She left several times and came back. So this was a mutual arrangement for her," Attorney Andy Hyde told WOIO. "I don't like that the federal prosecutors held a press conference to pat themselves on the back."

Attorneys representing Hunt and Brown could not be immediately reached by CNN for comment.

Prosecutor: 'They treated her worse than they treated the animals'

But a criminal complaint filed this week alleges that the mother and her daughter were padlocked inside the bedroom they shared.

"These individuals in this case preyed upon a human being's disability and her desire to protect her child, the most fundamental of human traits," Dettelbach said. The suspects "used that to force her into servitude, to work like an animal, and indeed, as the complaint alleges, they treated her worse than they treated the animals that were in that house."

Hunt and Callahan are a couple but are not married, FBI spokeswoman Vicki Anderson said. Brown was a friend of theirs, she said.

Before they were allegedly forced into servitude for two years, the victims knew their alleged captors, the law enforcement source said.

The woman was identified in court papers only as "S.E." Investigators stated Callahan and Hunt persuaded her to move into the apartment they shared with Hunt's four sons and "numerous" animals, knowing she "suffered from a cognitive disability and received monthly public assistance payments."

That was in May 2011. Her plight came to the attention of authorities in October 2012, when she was arrested for trying to steal a candy bar from a store. Then she was arrested on a state child-welfare charge as part of the case, Ashland Police Chief David Marcelli said.

"The officers that took that complaint detected that there was other issues aside from the shoplifting," Marcelli said. He said officers had had "numerous involvements" with the people involved, "and in the course of interviewing her, they discovered the rest of these facts slowly."

According to prosecutors, Callahan showed police a mobile-phone video of S.E. beating her child. S.E. told police that she had been told to do so by Callahan and Hunt and that Callahan threatened to show police the video if she "messed up" or went to authorities.

S.E. was released from jail in February after being sentenced to time served on the abuse charge, and her daughter is now in foster care, said Michael Tobin, a spokesman for the U.S. attorney's office.

Once the full picture emerged, Ashland police called in the FBI, "and shortly after, the suspects were indicted," Marcelli said.

'All of us...need to work on being better neighbors'

Callahan and Hunt kept tabs on the woman and child with a baby monitor, with Hunt taking the woman's government benefit cards, authorities said.

"Callahan and Hunt forced S.E. to clean the house, do laundry, walk to the store to do their shopping and care for their numerous pit bulls and reptiles," the prosecution statement said. Her child was kept in the apartment when she was sent to the store, they said.

Tuesday's announcement comes more than a month after the rescue of three women from a Cleveland home where police said a man had held them captive for about a decade.

Authorities believe there is no connection between the Ashland investigation and that case, the law enforcement source said.

Dettelbach, the federal prosecutor, said Tuesday's arrests are part of a broader push to crack down on what he called "modern-day slavery."

"We need your help in these efforts. Law enforcement cannot do it alone. All of us in the northern district of Ohio need to work on being better neighbors," he said. "We need to ask questions, hard questions, when we see something that doesn't look right. We need to not be afraid to pick up the phone and to call law enforcement. We need to not be afraid to ask those simple questions -- is everything OK? Is there some way I can help you? As Ohioans and as Americans, that is who we are, and it is our duty. "

CNN's Carol Cratty and Pamela Brown contributed to this report.