YAKIMA, Wash. — Kevin Harper did not fail a polygraph, and his ex-wife’s statement that he claimed he killed three people the same night the Goggin family was slain appears to be “coerced,” his lawyer says.

In court documents filed Thursday, Everett attorney Pete Mazzone accused Yakima County prosecutors of misrepresenting the results of a polygraph taken by his client in December.

Mazzone said a polygraph expert for the defense found his client’s answers weren’t deceptive, that the prosecution’s polygraph expert now agrees Harper wasn’t being deceptive, and that it was “patently false” for prosecutors to have said he was.

As for incriminating statements made by Crystal Gray-West, Harper’s now-ex-wife, Mazzone said he has not been able to interview her to determine if her statements can be verified.

“We do note preliminarily, however, that those statements appeared to have been coerced from her,” Mazzone wrote.

The filing was in direct response to potentially damaging documents filed by prosecutors two weeks ago that suggested Harper all but failed a polygraph about his role in the February 2011 bludgeoning deaths of Bill Goggin, owner of a Yakima civil engineering firm; his wife, Pauline; and his 98-year-old mother, Bettye. They were killed in what investigators believe was a burglary gone bad at their home in the gated Falcon Ridge community in Yakima’s West Valley.

Prosecutors filed the documents to bolster their attempt to revoke a plea deal they cut with Harper in October when the government’s case was crumbling under a series of missteps and accusations of misconduct against prosecutors and investigators.

A hearing has been scheduled for September to hash out the contractual issues surrounding the plea deal.

Prosecutors say new evidence justifies nullification of the plea deal on the grounds that Harper violated the underlying terms of an agreement that requires his truthful cooperation in the case.

But Mazzone now says prosecutors are the only ones violating the terms of the deal, which said information offered by Harper and Gray-West could not be used against them.

“The State has decided to inflame the passions of the community, and cover up their continued misconduct, by filing their most recent briefing on the subject,” he wrote.

In addition to the results of the polygraph, prosecutors had also filed a transcript of an interview with sheriff’s detectives in November in which Gray-West tearfully claimed Harper told her the same night the Goggins were slain that he had killed three people during a burglary.

That explosive statement and Harper’s polygraph exam came weeks after Harper, 31, signed the plea deal, allowing him to plead guilty to relatively minor theft and firearm charges rather than face triple-murder charges.

Under the arrangement, Harper pleaded guilty to first-degree unlawful possession of a firearm and second-degree possession of stolen property related to the theft of a Western-style .22-caliber pistol from the Goggin home.

In exchange, prosecutors agreed to recommend a prison sentence of just over seven years. They also agreed to drop the murder charges when Harper was sentenced.

He hasn’t been sentenced yet, however.

• Chris Bristol can be reached at 509-577-7748 or cbristol@yakimaherald.com. Follow him on Twitter at twitter.com/ChrisJBristol.