A Utah woman was convicted on Monday of aggravated murder after poisoning her husband with fentanyl and then self-publishing a children’s book about coping with grief.

Prosecutors said Kouri Richins slipped five times the lethal dose of the synthetic opioid into a cocktail that her husband Eric Richins drank in March 2022.

Prosecutors said she was $4.5m in debt and falsely believed that when her husband died, she would inherit his estate worth more than $4m. They also said she was planning a future with another man she was seeing on the side.

“She wanted to leave Eric Richins but did not want to leave his money,” the Summit County prosecutor, Brad Bloodworth, said.

Richins stared at the floor and took deep breaths as the judge read the verdict.

The jury deliberated for just under three hours. Afterwards, family members on both sides of the case left the courtroom hugging and crying.

Richins was also convicted of other felonies, including an attempted murder charge in what authorities alleged was another effort to poison her husband weeks earlier on Valentine’s Day with a fentanyl-laced sandwich that made him black out. Jurors also found Richins guilty of forgery and fraudulently claiming insurance benefits after his death.

Sentencing was scheduled for 13 May, the day her husband would have turned 44. The aggravated murder charge alone carries a sentence of 25 years to life in prison.

“Honestly I feel like we’re all in shock,” said Eric Richins’ sister, Amy Richins. She said the family can now focus on honouring her brother and supporting his sons. “We got justice for my brother.”

The scheduled five-week trial was cut short last week when Kouri Richins waived her right to testify, and her legal team abruptly rested its case without calling any witnesses.

Richins’ lawyers said they were confident that prosecutors did not produce enough evidence to convict her of murder.

Prosecutors said Richins, a real estate agent focused on flipping houses, was deep in debt. She had opened numerous life insurance policies on her husband without his knowledge, with benefits totalling about $2m, prosecutors alleged.

They showed the jury text messages between Richins and Robert Josh Grossman, the man with whom she was allegedly having an affair, in which she fantasised about leaving her husband, gaining millions in a divorce and marrying Grossman.

The internet search history from Richins’ phone included “what is a lethal.dose.of.fetanayl”, “luxury prisons for the rich America” and “if someone is poisned (sic) what does it go down on the death certificate as”, a digital forensic analyst testified.

Bloodworth replayed for the jury a clip of Richins’ 911 call from the night of her husband’s death. That’s “not ‘the sound of a wife becoming a widow’,” he said, quoting the defence’s opening statement. “It’s the sound of a wife becoming a black widow.”