SPRINGFIELD -- A married couple pleaded guilty Wednesday to criminal charges in connection with running an interstate prostitution ring that drew in several women -- one of whom told federal agents the couple insisted they deposit their proceeds in a snake tank.

Which, lawyers in the case confirmed, was not street slang but an actual serpent coiled up in a glass tank to deter anyone tempted to steal the cash.

Milford and Tiana Lewis, 36 and 32, respectively, of Springfield, pleaded guilty in U.S. District Court to multiple counts of inducing travel to engage in prostitution and making extortionate threats.

Federal prosecutors agreed to dismiss human trafficking charges at sentencing and spare the defendants 15-year mandatory minimum sentences. In exchange, Milford Lewis agreed to serve 12 years in prison and his wife six.

However, U.S. District Judge Mark G. Mastroianni has the discretion to sentence as he sees fit at the couple's upcoming joint sentencing hearing.

The couple insisted that their pleas be linked, specifying in their respective agreements that they reserve the right to withdraw their pleas if either sentence is rejected by the judge.

The Lewises, who were newly married at the time, were arrested in the parking lot of a Springfield strip club in December 2015 when several women complained to local and federal authorities that they were being threatened by the couple after being recruited to work for a company, called Sinful Innocence, billed as a "talent agency" in online ads.

Unnamed witnesses labeled by Assistant U.S. Attorney Alex J. Grant "Females A through H," mostly from Connecticut, said they answered online ads and met with the couple, who said they were "CEOs" of the firm.

The women signed boilerplate contracts that included a $350 "separation fee" if the employees bailed out.

Some met the Lewises in the food court of Tower Square in Springfield to sign "employment agreements" while others were ushered by a driver to one of two motels in West Springfield where the couple ran the true lion's share of their business: turning tricks.

All the witnesses cited by Grant in Wednesday's hearing said the couple muscled or attempted to manipulate them into prostitution. In some cases they were successful and instructed the women to charge between $75 and $200 depending on the length of the "sessions."

The Lewises initially promised to split the proceeds with the women who acquiesced to prostitution, but one said they paid her nothing aside from beer, drugs, cigarettes and limited amounts of food, plus allowed her to stay in their hotel room.

One witness told federal agents they were instructed to deposit any payments in the snake tank in the hotel room, Grant told Mastroianni.

That woman, "Female E," said she agreed to let the Lewises find stripping and singing gigs for her, and that she had been in the escort business before but wanted to put it behind her. When she left, the couple began threatening to kill her and her son over the $350 separation fee.

Another, "Female F," was among the victims who received a ride to a hotel and had no way to get home, Grant said. When she attempted to leave, Tiana Lewis charged her and began beating her.

Once an ex-boyfriend agreed to come pick the woman up, Tiana Lewis began beating her again, the prosecutor said. Milford Lewis came out to the parking lot with a BB gun that resembled a real gun, but the woman's ex responded: "Do something and I'll have the police flooding this place."

Female F said that after she was able to escape the couple, they called her up to 20 times a day demanding the $350.

"Milford Lewis told her his 'bitches' were going to f--- her up," unless she paid the $350 or worked it off turning tricks, Grant said.

The sentencing is set set for Nov. 16.