A Utah mother who published a children’s book about grief after the death of her husband and was later found guilty of killing him has been sentenced to life in prison without the possibility of parole.

Kouri Richins was convicted in March of aggravated murder for lacing her husband’s cocktail with five times the lethal dose of fentanyl at their home near Park City in 2022.

“A person convicted of those things is simply too dangerous to ever be free,” Judge Richard Mrazik said, when handing down the sentence on the day her late husband, Eric Richins, would have turned 44.

Prosecutors said Richins, a 35-year-old real estate agent with a house-flipping business, was millions in debt and planning a future with another man. She had opened numerous life insurance policies on Eric Richins without his knowledge and falsely believed she would inherit his estate worth more than $4m after he died.

Jurors in Park City also found Richins guilty of four other felonies, including attempted murder for trying to poison her husband weeks earlier on Valentine’s Day with a fentanyl-laced sandwich.

Richins has been adamant in maintaining she is innocent, saying on Wednesday that the verdict was “an absolute lie”.

Her case captivated true-crime enthusiasts when she was arrested in 2023 while promoting her children’s book Are You With Me? about a boy coping with the death of his father.

Richins wore a lime green jail uniform and chatted with her lawyers on Wednesday morning while Eric Richins’ family members passed around pocket-size packs of tissues. Her lawyers declined to comment before the hearing.

Eric Richins’ sister, Amy Richins, said after the verdict that she was “just very happy that we got justice for my brother” and could now focus solely on supporting his sons, who were ages nine, seven and five when their father died.

In a memo filed by prosecutors ahead of the hearing, the sons told the judge they would feel unsafe if their mother was ever released from prison.

“I’m afraid if she gets out, she will come after me and my brothers, my whole family,” said the oldest boy, who is now 13. “I think she would come and take us and not do good things to us, like hurt us.”

The middle child, now 11, said he was sad that his dad won’t be present for major milestones. With his mother behind bars, he said he can “live a happy and successful life without fear of [her] hurting me or anyone I love”.

The youngest said he would be “so scared” if his mother was released.

The trial was scheduled for five weeks but ended early when Richins waived her right to testify, and her legal team rested its case without calling any witnesses. Her attorneys said they were confident that prosecutors had not produced enough evidence to convict her of murder.

Throughout the trial, prosecutors portrayed the mother of three as a money-hungry killer. They showed the jury text messages between Richins and her lover in which she fantasized about leaving her husband and gaining millions in a divorce. Prosecutors also displayed the internet search history from Richins’ phone, which included queries about the lethal dose of fentanyl, luxury prisons and how poisoning is marked on a death certificate.

Associated Press contributed reporting