Chantale Youngblood, 20, pleaded guilty to four Class A felonies of second-degree murder before Presiding Circuit Judge Gael Wood in Franklin County, according to her attorney, Steve Lynxwiler with the Public Defender's Office.
Youngblood entered her plea during what was supposed to be her pretrial conference and after the state, represented by Assistant Attorney General Kevin Zoellner, filed an amended information with the court charging her with the lesser crimes.
The information accused Youngblood, either acting alone or knowingly in concert with another, of knowingly causing the deaths of Loyd Eugene Piatt, 77, and Gladys Irene Piatt, 80, on June 23, 2010, and Edgar Atkinson, 81, and Bonnie Chase, 69, on July 10, 2010, by shooting them.
Youngblood, who earlier was granted a change of venue to Franklin County in her case, was to stand trial July 29 through Aug. 2 on four Class A felonies of first-degree murder.
Zoellner had dismissed the four unclassified felonies of armed criminal action (ACA) Youngblood was facing earlier this month.
After entering her plea, Lynxwiler said, his client waived having a sentencing assessment report be completed by Probation and Parole.
Pursuant to the plea negotiations, Lynxwiler said, the state is recommending concurrent 20-year sentences on each count.
Lynxwiler said Youngblood is to be sentenced at 3:30 p.m. Aug. 26 on one of the counts, with sentencing on the remaining counts to be at a later date.
That sentencing recommendation, according to the plea petition filed with the court, is contingent upon Youngblood's "truthful testimony" in the state's prosecution of Youngblood's then boyfriend, Keith A. Boyles, for his alleged role in the crimes.
Boyles, 21, is charged with four Class A felonies of first-degree murder and four unclassified felonies of ACA.
Boyles, who could face the death penalty if he is convicted of the murders, is to stand trial in 2014.
A jury will be selected from Ste. Genevieve County on May 1-2 to hear the case in Butler County, with testimony set to begin on May 5.
Youngblood's parents already are serving sentences in the Missouri Department of Corrections for their roles in the murders.
A Shannon County jury convicted Youngblood's mother, Melissa "Lisa" Youngblood, of two Class A felonies of first-degree murder in connection with Atkinson and Chase's death in January. The 36-year-old is serving concurrent life sentences and is not eligible for probation or parole.
In June 2012, her father, David Youngblood, 49, pleaded guilty as charged to the four Class A felonies of first-degree murder. He is serving consecutive life sentences on each charge and is not eligible for probation or parole.
Four ACA charges were dismissed by the state at the time of David Youngblood's plea and sentencing.
The Youngbloods, their then 17-year-old daughter and Boyles initially were charged in connection with the deaths of Atkinson and Chase, who were found in their burning Current View, Mo., home.
An autopsy determined Atkinson died of gunshot wounds to the head and upper torso. A cause of death for Chase was not immediately known.
The father and daughter, as well as Boyles, subsequently also were charged with killing the Piatts, who were David Youngblood's aunt and uncle. The Piatts were found dead inside their rural Doniphan home June 23, 2010.
While authorities initially thought the couple had died of smoke inhalation, they became suspicious when David Youngblood was among those arrested in connection with the deaths of Atkinson and Chase.
After the Youngbloods and Boyles were charged in connection with the couple's deaths, the investigation into the Piatts' deaths was re-opened.
As part of that investigation, the Piatts' bodies were exhumed, so autopsies could be performed to determine how they died. Both reportedly had been shot in the chest.
Testimony from Melissa Youngblood's January trial indicated David Youngblood wanted Boyles and his daughter to "kill the Piatts and burn their house" as a "trial run" because "he wanted people to help him" rob banks.
The witness said David Youngblood wanted to make sure Boyles and his daughter could commit the crime, and he dropped the then teenagers off near the Piatts' home. Boyles allegedly was armed with a 9mm handgun.
Using gasoline found at the Piatt home, the teens then allegedly set the house on fire.
Additional testimony indicated Atkinson and Chase's subsequent deaths were "another trial run" for the bigger plan David Youngblood and others hoped to carry out.