A judge on Friday found a Missouri man guilty of murder in the shooting deaths of two elderly couples who authorities say were killed as part of two tests ahead of another man's "grandiose plan" to rob a local bank by kidnapping its president.

Judge Michael Pritchett found Keith Boyles, 26, guilty of four counts of first-degree murder and four counts of armed criminal action, KFVS-TV reports . He faces life in prison without the possibility of parole for the 2010 deaths of 80-year-old Gladys Irene Piatt; her 77-year-old husband, Loyd Eugene Piatt; 81-year-old Edgar Atkinson; and 69-year-old Bonnie Chase.

According to prosecutors, the deaths were part of David Youngblood's plan to force the president of a local bank to open the vault, then use the money to move his family to a country that would not extradite them. At the time of the slayings, Boyles was dating Youngblood's daughter, Chantale Youngblood, and living in the family's home, according to news release from Missouri Attorney General Eric Schmitt's office. The bank robbery never happened.

David Youngblood tasked his daughter and her boyfriend with killing the Piatts, who were David Youngblood's aunt and uncle, as a "test" to see if they would carry out violent crimes, the attorney general's office said. Prosecutors alleged at trial that Boyles shot and killed the Piatts on June 23, 2010. Authorities initially thought the Piatts died of smoke inhalation after their bodies were found inside their burned Ripley County home.

Boyles and David Youngblood killed Atkinson and Chase two weeks later during a second "test run," the attorney general's office said. Boyles was accused of shooting and killing Atkinson while David Youngblood shot and killed Chase. Atkinson and Chase were also found in a burned home. After those deaths, authorities exhumed the Piatts' bodies and discovered they, too, had been shot to death.

Youngblood is serving life in prison after pleading guilty to first-degree murder in 2012. His wife, Melissa Youngblood, is serving life in prison after being convicted of first-degree murder in 2013. Chantale Youngblood faces sentencing on April 18 after pleading guilty to four counts of second-degree murder. Boyles' sentencing is set for May 1.

Boyles' first trial in January 2016 ended in a mistrial when prosecutors could not seat a jury. Boyles agreed to a bench trial in exchange for prosecutors taking death penalty off the table as a possible punishment.

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Information from: KFVS-TV, http://www.kfvs12.com