Kouri Richins' husband was found dead at the foot of their bed last March.

She'd just closed on a house for her business, she told investigators at the time. Around 9 p.m., she brought her husband, Eric Richins, a celebratory Moscow Mule cocktail in the bedroom of their home in Kamas, Utah.

She left to sleep with their son in his room and returned around 3 a.m. to find her husband lying on the floor cold to the touch, she told authorities. About a year to the day her husband died, Richins published a children's book, "Are You With Me?" about navigating grief after the loss of a loved one.

But investigators now allege she killed her husband of nine years with a lethal dose of illicit fentanyl. This month, they charged her with aggravated murder and three counts of possession of a controlled substance with intent to distribute.

Newly released court documents detailed a series of illicit fentanyl purchases in the months leading up to his death.

Kouri Richins, 33, allegedly bought the drugs from an acquaintance identified as C.L. in court documents. Weeks before her husband's death, the Richins had marked Valentine's Day with a dinner at home.

"Shortly after the dinner, Eric became very ill. ... Eric told a friend that he thought his wife was trying to poison him," court documents say.

Kouri Richins was arrested Monday and remains in custody. CNN has reached out to her attorneys for comment.

He had a lethal dose of fentanyl in his system

An autopsy and toxicology report revealed that Eric Richins, 39, died of a fentanyl overdose. He had about five times the lethal dosage in his system, according to a medical examiner.

Investigators obtained a search warrant and seized his wife's phone and several computers in their home. They discovered communications between Kouri Richins and C.L., who had an extensive police record that included drug-related offenses, court documents say.

C.L. told detectives that at some point between December 2021 and February 2022, Kouri contacted C.L. and asked for prescription pain pills for an investor. C.L. said they obtained hydrocodone and left the pills at a property Kouri was flipping, picking up cash left for them, court documents say.

A couple of weeks later, Kouri Richins reached out again and asked for "some of the Michael Jackson stuff," according to court documents. Kouri Richins allegedly went to C.L.'s house around February 11 and paid $900 for "15-30 fentanyl pills" that C.L. had obtained from a dealer.

About two weeks later, on February 26, she allegedly reached out to C.L. for more fentanyl pills. C.L. left them at an outdoor fire pit at the same property where the hydrocodone had been delivered. Again, the money was left there for pickup. By this time, according to court documents, Kouri Richins no longer owned the property.

He died six days after alleged pill delivery

About 3:30 a.m. on March 4, 2022, Summit County Sheriff's deputies and EMS personnel responded to a report of an unresponsive man at the couple's home.

First responders unsuccessfully tried to revive Eric Richins. It was six days after the latest alleged pill delivery.

His wife gave investigators her version of what happened that night. The couple was celebrating closing on a house for her business and she brought him a cocktail in bed. Kouri Richins said she left him in the room and went to sleep with one of her three sons in his room because the child was "having a night terror," court documents say.

"Defendant said she awoke around 03:00 hours and came back to her and Eric's bedroom. She felt Eric and he was cold to the touch. That is when defendant called 911," court documents say.

Kouri Richins allegedly told law enforcement officials that she left her phone plugged in next to her bed and did not take it to her son's room.

"However, between when the defendant said she went to child's room and when she called 911, the status on her phone shows that it was locked and unlocked multiple times and there was also movement recorded on the phone. In addition, tolls on defendant's phone show that messages were sent and received during that time. These messages were deleted," court documents say.

For months, Kouri Richins worked on her book. Last month, she appeared on "Good Things Utah," a show on local television station ABC4, to talk about the importance of her children's book on mourning.

She said it's based on three concepts: connection, continuity and care.

"Connection: Keep the person's spirit alive who has passed. ... Continuity: Try and keep routines and schedules as normal as possible. ... Care: Affirming their feelings; understanding when they are sad, mad, lonely and talking about those feelings and letting them know it's OK," Kouri Richins said in the interview.

Her three young sons helped her write the book to help them articulate their feelings, she said.

Weeks later, Kouri Richins was arrested in her husband's death.

Her detention hearing is set for May 19.