Ron Lafferty, 78, was convicted in 1996 for the 1984 slayings of his sister-in-law Brenda Lafferty, 24, and her 15-month-old daughter Erica

A Utah death row inmate featured in the popular book ‘Under the Banner of Heaven’, after killing his sister-in-law and her child for resisting his polygamist beliefs, inched closer to becoming the first American to be executed by firing squad in nearly a decade after losing his latest appeal Monday.

Ron Lafferty, 78, could be executed as soon as next year after his latest legal setback, said Andrew Peterson, assistant solicitor general at the Utah attorney general’s office.

Lafferty’s lawyer, Dale Baich, said in an email that he will use all options to challenge the ruling and will probably ask the U.S. Supreme Court to review the case.

‘When the most severe penalty a state can impose is at stake,’ Baich said, ‘we look to the courts to be the safety net to ensure that the full protections allowed by the Constitution have been met. Here, the court relied on procedural technicalities to deny Mr. Lafferty a complete appellate review of his case.

‘We are carefully reviewing the decision and going forward, we will exercise all state and federal legal options.’

Lafferty could be executed as soon as next year after his latest legal setback, said Andrew Peterson, assistant solicitor general at the Utah attorney general’s office

Along with his brother Dan, Lafferty brutally murdered his sister-in-law Brenda Lafferty, 24, and her 15-month-old daughter Erica (both shown above, with Lafferty's other brother, Allen)

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Utah has not executed an inmate by firing squad for nearly 10 years, since Ronnie Lee Gardner was administered the fatal procedure in June 2010, having murdered an attorney during a failed courthouse escape.

The state currently has eight inmates on death row, with Monday’s ruling making Lafferty the closest of them to meeting his fate.

Along with his younger brother Dan, Lafferty was convicted for the 1984 slayings of his sister-in-law Brenda Lafferty, 24, and her 15-month-old daughter Erica.

According to court documents, the brothers blamed Brenda for helping Lafferty’s wife leave him with their six children.

They were also reportedly incensed that she allegedly forbade her husband, Allen Lafferty, from joining their polygamous cult called the School of Prophets.

Utah has not execute an inmate by firing squad for nearly 10 years, since Ronnie Lee Gardner (left) was administered the fatal procedure in June 2010, having murdered an attorney during a failed courthouse escape. The state currently has eight inmates on death row, with Monday’s ruling making Lafferty (right) the closest of them to meeting his fate

The use of firing squad was terminated in 2015, with new legislation ruling it would only be used an execution method when lethal injection drugs weren’t otherwise available (pictured: Utah's firing squad execution chamber)

As a result, on Pioneer Day 1984, the Lafferty brothers forced their way into the couple’s American Fork duplex while Allen was not home.

Lafferty and Dan beat Brenda, strangled her with a vacuum cord and then slit her throat. Erica was also killed with a slit to her throat, records show.

The two brothers were tried separately, with Dan going first in January 1985. He represented himself and jurors later convicted him of two counts of first-degree murder and four other felonies, but a vote for the death sentence couldn’t be reached unanimously and he was instead sentenced to life.

However, Ron Lafferty, represented by lawyers, went to trial the following April and a unanimous verdict for the death sentence was reached, following his conviction.

The 10th Circuit later overturned the capital murder conviction and ordered a new trial in 1996, after finding that the wrong standards had been used to evaluate Ron Lafferty’s mental competency – however the same verdict was reached.

Upon the conclusion of the trial, the 78-year-old chose death by firing squad as his execution method.

At the time, the state offered death row inmates a choice between the firing squad and lethal injection, but Lafferty has since changed his mind.

Lafferty and Dan (left) beat Brenda, strangled her with a vacuum cord and then slit her throat. Erica was also killed with a slit to her throat, records show

According to court documents, the brothers blamed Brenda for helping Lafferty’s wife leave him with their six children. They were also incensed that she allegedly forbade her husband, Allen Lafferty (right), from joining their polygamous cult called the School of Prophets

The use of firing squad was terminated in 2015, with new legislation ruling it would only be used an execution method when lethal injection drugs weren’t otherwise available.

However, as Lafferty selected the firing squad long before the law change was introduced, he’s not privy to its terms according to the courts.

To soften their stance, during Monday’s appeal hearing Lafferty re-aired some old arguments, in which he claimed his attorney’s at his original trial misrepresented him, that he wasn’t of sound mind at the time of his trial and he should not have been made to stand trial for a second time after winning an earlier appeal.

Lafferty’s lawyers have argued that he suffered from mental illness, and his punishment was out of line with the life sentence given to his brother.

The two brothers were tried separately, with Dan (pictured left in 2003) going first in January 1985. He represented himself and jurors later convicted him of two counts of first-degree murder and four other felonies, but a vote for the death sentence couldn’t be reached unanimously and he was instead sentenced to life. However, Ron Lafferty, represented by lawyers, went to trial the following April and a unanimous verdict for the death sentence was reached, following his conviction

However, the U.S. 10th Circuit Court of Appeals in Denver backed lower court judges in their previous rejections of the arguments

Peterson, the prosecutor, said he’s pleased Lafferty’s countless appeals have nearly run their course. He said he considers it a long shot that the U.S. Supreme Court would take the case, despite suggestions that Lafferty may yet argue he’s not competent to be executed.

‘Five judges have said there’s nothing in this case worth spending any more time on,” Peterson said.

He added there is a different legal standard for determining if someone is competent to go to an execution chamber.

‘As long as he knows why he’s being punished,’ Peterson said, ‘he’s competent to be executed.'