The Florida woman who created an elaborate conspiracy to murder her mother-in-law for the inheritance money has pleaded guilty to first-degree murder and to witness tampering, Rockland County District Attorney Thomas Zugibe announced.

After driving to Rockland County with a friend, Diana Nadell persuaded Peggy Nadell to open the door of her Valley Cottage home and then bludgeoned, stabbed and strangled her.

The witness-tampering relates to Diana Nadell's attempt to silence two of three co-conspirators who had already pleaded guilty to a reduced charge.

"Peggy Nadell was a caring mother and grandmother and a respectable and benevolent member of the community here in Rockland County," Zugibe said in his announcement. "In an ultimate act of betrayal, her life was cut short by her vicious and violent murder at the hands of her own daughter-in-law. Today's guilty plea brings justice to Diana Nadell, the person whom, motivated by greed, orchestrated and carried out this heinous plot to murder Peggy Nadell."

• One count of Attempted Tampering with a Witness in the First Degree.

"Peggy Nadell was a caring mother and grandmother and a respectable and benevolent member of the community here in Rockland County," said District Attorney Zugibe. "In an ultimate act of betrayal, her life was cut short by her vicious and violent murder at the hands of her own daughter-in-law. Today's guilty plea brings justice to Diana Nadell, the person whom, motivated by greed, orchestrated and carried out this heinous plot to murder Peggy Nadell."

On January 25, 2014, at approximately 10 a.m., Peggy Nadell was found murdered in her home at 644 Andover Road, Valley Cottage, New York.

An extensive investigation by the Clarkstown Police Department and the Rockland County District Attorney's Office revealed that on January 24, 2014, Diana Nadell travelled to Washington, D.C.. Once there, Nadell allegedly offered Benson money to drive with her to New York to assist in the killing of her mother-in-law, Peggy Nadell.

Upon arriving at 644 Andover Road after 1 a.m. on January 25, Diana Nadell and Andrea Benson murdered Peggy Nadell. Peggy Nadell suffered strangulation, multiple blunt force trauma wounds to her head and face as well as multiple stab wounds to her torso, ultimately causing her death.

It is alleged that Tanisha Joyner (DOB 05/02/88) of 1538 Butler Street SE 303, Washington, DC. and Eltia Grant (DOB 10/08/89) of 1050 Gladys Avenue, Apt. 7, Long Beach, California rendered criminal aid to Diana Nadell. It is further alleged that Joyner provided Clarkstown Police a false alibi, later telling detectives Diana Nadell was with her in Washington, D.C. during the evening hours of January 24, 2014 through the early morning hours of January 25, 2014. Grant allegedly acted as a go-between for Diana Nadell and Benson in aiding in the logistics and specifics of the false alibi.

On May 30, 2014, Joyner pleaded guilty to Hindering Prosecution in the First Degree, a class "D" Felony. Her sentence is pending.

On June 17, 2014, Grant pleaded guilty to Hindering Prosecution in the Second Degree, a class "E" Felony. Her sentence is pending.

On June 19, 2014, Andrea Benson was arraigned before Hon. William A. Kelly on the above indictment. Andrea Benson then entered a plea of guilty to the crime of Murder in the Second Degree and in doing so admitted that she and Diana Nadell entered 644 Andover Rd., Valley Cottage, New York in the early morning hours of January 25, 2014 and murdered Diana Nadell.

Her promised sentence is 20 years to life in prison. This promise is conditioned on her adherence to the conditions of an agreement she has reached with the Rockland County District Attorney's Office.

While incarcerated at the Orange County Jail on the murder indictment, Nadell contacted another inmate whom she believed was being deported to Jamaica and solicited the inmate to participate in a plot to murder two of the cooperating witnesses she believed would provide crucial testimony against her at trial. Members of the Clarkstown Police Dept., Rockland County District Attorney's Office, the Orange County Sheriff's Department and the Orange County District Attorney's Office conducted an investigation and Nadell was thereafter indicted on multiple charges, including Attempted Tampering with a Witness in the First Degree.

As part of the plea agreement, Nadell will be sentenced to 23 years to life in state prison when she is sentenced on May 12, 2015. She will receive a concurrent maximum sentence of five to fifteen years on the tampering plea.

This cases were prosecuted by Supervising Assistant District Attorney Richard Kennison Moran and Assistant District Attorney Patrick Fischer.