Federal prosecutors alleged a third murder plot Monday in connection with the killing of a Florida millionaire in a suburban New York hotel.

"We have learned of efforts to kill another witness," assistant U.S. Attorney Elliott Jacobson said during the arraignment of the victim's widow, Narcy Novack, 53, of Fort Lauderdale.

Jacobson did not identify the witness or say who was behind the alleged plot, but he mentioned it while arguing against bail for Novack.

Novack, her brother and three other men were charged last month in the death of her husband, Ben Novack Jr., who was found beaten to death at the Hilton in Rye Brook in July 2009. His company had organized an Amway convention at the hotel.

Prosecutors say Novack let two killers into the hotel room, watched as they beat her husband with dumbbells and ordered them to cut his eyes out. On Monday, Jacobson called the killing "extraordinarily grisly."

Novack pleaded not guilty on Monday in her first court appearance since being brought to New York for trial.

She was accused in a second killing when she appeared in court in Florida after her arrest. Jacobson alleged then that she plotted the beating death of her 86-year-old mother-in-law three months before her husband's killing.

Jacobson said Narcy Novack wanted to inherit millions of dollars stemming from the estate of her late father-in-law, Ben Novack Sr., who built the famed Fontainebleau Hotel in Miami Beach.

She has not been charged in the mother-in-law case.

The third plot came to light on Monday after Novack's attorney, Howard Tanner, asked Magistrate Judge Paul Davison to allow Novack free on bail, saying she would agree to any conditions, including electronic monitoring.

Jacobson fought that suggestion, again saying that Novack had been implicated in the killing of the mother-in-law. He also suggested that the "Veliz family" — Veliz is Novack's maiden name and her brother is Cristobal Veliz — had plotted to frame and assault Novack's daughter, May Abad, who stands to inherit the estate if Novack is convicted in the killing.

Then Jacobson disclosed the alleged plot against the unidentified witness.

A call to the U.S. attorney's office seeking details of the plot was not immediately returned.

Novack's lawyer, Howard Tanner, said it was unfair "for the government to throw out a serious allegation like that" without backing it up in a formal charge. He said he had no information on the alleged plot

"The government will simply throw out allegations that are not based on any fact," he said. "Anyone can say anything they want about plots but there is going to come a time, and it will come at the trial, where they're going to have to be put to their proof."

Magistrate Judge Paul Davison ruled against bail, saying he did so without considering any uncharged allegations. The formal charges in the indictment are conspiracy to commit interstate domestic violence and stalking. Novack faces a potential life sentence if convicted.