(CNN) -- A puppy was used to lure two Amish girls into a car in upstate New York, with the captors plotting to enslave the sisters, authorities said.
Nicole Vaisey, 25, told investigators that she and her boyfriend, Stephen Howells II, 39, were on a "shopping trip" for "slaves" when they allegedly kidnapped the girls, according to a detective.
The girls were picked up at a vegetable stand outside the sisters' family farm about 50 miles from the Canadian border on August 13.
New details about the abduction in Oswegatchie emerged during a preliminary hearing in St. Lawrence County on Thursday. Detective Sgt. Brooks Bigwarfe detailed the couples' alleged plan and kidnapping of the girls, as related to him by Vaisey.
"They had been planning this for several weeks," Bigwarfe said.
Howells and Vaisey drove to the farm, pulled up to the stand in a location where they couldn't be seen, and waited for the girls -- ages 6 and 12 -- to approach the car, Bigwarfe said. Howells allegedly scoped out the stand the previous week.
Howells asked the girls whether they wanted to pet the dog, a Doberman pinscher-golden retriever mix named Kaleidoscope, police said. When the older sister grew suspicious, Bigwarfe said, Howells pushed the girls into the back of the car.
"When he started forcing them into the vehicle, they were both screaming and yelling," Bigwarfe said.
The girls were held captive for nearly 24 hours, during which they were handcuffed together, shackled to a bed and sexually abused, according to the sheriff's department.
With widening media coverage, a large police response in the area and an Amber Alert, though, Bigwarfe said the couple began to worry and decided it was too risky to keep the girls.
Howells abandoned the two girls in an isolated area 12 miles from where they were being held, Bigwarfe said.
"There's no doubt in my mind that if they were successful they were going to continue with future acts," said Mary Rain, district attorney for St. Lawrence County.
Howells' attorney, Amy Dona, declined to comment Friday.
Vaisey appeared at the hearing wearing a bulletproof vest, according to her lawyer, Bradford Riendeau.
Riendeau alleged his client was in a master-slave relationship with Howells and that she was not the mastermind of the planned kidnapping.
"I don't think she had any control over what went on in the relationship. That was the essential ground rule of it," Riendeau alleged. "He told her what to do."
Fowler Township Justice Paul Lamson ruled that there was reasonable cause to believe Vaisey committed a felony and ordered her held without bail.
Howells waived his right to a hearing and did not appear in court Thursday. Howells also was being held without bail, Riendeau said.
The two were charged with second-degree kidnapping and face up to 25 years in prison if convicted, according to Riendeau.