A self-published romance novelist who once wrote an essay titled How to Murder Your Husband has been convicted in the US state of Oregon of fatally shooting her spouse.

A jury of seven women and five men found Nancy Crampton Brophy, 71, guilty of second-degree murder on Wednesday after deliberating for two days over chef Daniel Brophy’s death, Portland’s KOIN-TV reported.

Mr Brophy, 63, was killed on June 2, 2018, as he prepped for work at the Oregon Culinary Institute in south-west Portland.

Lisa Maxfield, one of Crampton Brophy’s lawyers, said the defence team plans to appeal.

Prosecutors told jurors Crampton Brophy was motivated by money problems and the prospect of cashing in a life-insurance policy.

Crampton Brophy said during the trial, however, she had no reason to kill her husband and their financial problems had largely been solved by cashing in a chunk of his retirement savings plan.

She owned the same make and model of gun used to kill her husband and was seen on surveillance camera footage driving to and from the culinary institute, court exhibits and testimony showed.

Police never found the gun that killed Mr Brophy.

Prosecutors alleged Crampton Brophy swapped out the barrel of the gun used in the shooting and later discarded it.

Defence lawyers said the gun parts were inspiration for Crampton Brophy’s writing and suggested someone else might have killed Brophy during a robbery gone wrong.

Crampton Brophy testified during the trial that her presence near the culinary school on the day of her husband’s death was mere coincidence and she had parked in the area to work on her writing.

The would-be writer’s how-two treatise detailed various options for committing an untraceable killing and professed a desire to avoid getting caught.

Circuit Judge Christopher Ramras excluded the essay from the trial, noting it was published in 2011.

A prosecutor, however, alluded to the essay’s themes without naming it after Crampton Brophy took the stand.

Crampton Brophy has remained in custody since her arrest in September 2018, several months after her husband was shot.