Associated Press

SALT LAKE CITY — 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 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 likely ask the U.S. Supreme Court to review the case.

Lafferty chose the firing squad decades ago when he was sentenced to die — before Utah changed its law to use it only as a backup method if lethal injection drugs aren't available.

The last time a firing squad was used in the U.S. was in 2010, when Ronnie Lee Gardner was executed in Utah for the 1984 murder of an attorney during a failed courthouse escape.

Lafferty was convicted in the 1984 slayings of his sister-in-law and her baby daughter, which he carried out with his brother. He claimed to get a revelation from God to kill the two because of her resistance to his fundamentalist beliefs in polygamy.

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His case became well known nationwide when it was included in Jon Krakauer's 2003 book about radical offshoots of The Church of Jesus Christ of Latter-day Saints. Krakauer also wrote the popular books "Into Thin Air" and "Into the Wild."

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 Dan Lafferty, among other objections.

The ruling Monday by the 10th U.S. Circuit Court of Appeals in Denver backed lower-court judges in their previous rejections of the arguments.

His lawyer, Baich, expressed disappointment that the court relied on what he described as "procedural technicalities" to deny Lafferty a complete review of his case.

"When the most severe penalty a state can impose is at stake, we look to the courts to be the safety net to ensure that the full protections allowed by the constitution have been met," Baich said in a statement.

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.

"Five judges have said there's nothing in this case worth spending any more time on," Peterson said.