Jason Harris appears in court in Genesee County, Mich., on Tuesday with his attorney. (ABC12)

The cereal kept reappearing in Jason Harris’s account of his wife’s unusual death, but for years, no one knew how it fit in.

The neighbor who found her body was the first to hear of it. Harris called her the morning of Sept. 29, 2014, saying he was worried about his wife, Christina Ann-Thompson Harris, and wondered if the neighbor could check on her. Christina was coughing and sleeping restlessly when he left their home in Davison, Mich., that morning, he said. The night before, she was feeling weak but very hungry and so he poured her a bowl of cereal. She tried to eat it, he said, until she dropped the bowl on the floor and fell out of her chair, passing out. When the neighbor went to check on her, she found her in the bed where Harris had left her.

Christina, a 36-year-old mother of two, was dead.

But the autopsy would raise more questions than answers. The Genesee County Medical Examiner’s Office ruled the next month that Christina died of an accidental heroin overdose.

Neither her closest friends nor her co-workers at the Subway location she managed knew Christina to use drugs, let alone heroin, Genesee County Prosecutor David Leyton said at a Tuesday news conference. The “incredibly loving mother” was still breast-feeding the couple’s 4-month-old baby, Leyton said, and even Harris told police his wife was very careful about the substances she put into her body. She was supposed to go to an appointment with her OB/GYN that morning, so why would she be getting high on heroin?

Police weren’t convinced she would, either, and kept the case open. Now, after five years of investigating, authorities say they finally know what really killed Christina: the bowl of cereal — which her husband had spiked with heroin.

On Tuesday, Harris was arrested at the home where his wife died and charged with first-degree premeditated murder, solicitation of murder and delivery of a controlled substance causing death. Leyton said investigators tested Christina’s breast milk, which was recovered at her parents’ home in three plastic packages and then frozen for years, and “in each instance,” he said, “no controlled substance was found.” It was the first time in Michigan’s history that a prosecutor asked the crime lab to test breast milk, Leyton said.

Late last week, he said, the coroner amended Christina’s cause of death to homicide.

Harris’s defense attorney, Nicholas Robinson, told The Washington Post that his client pleaded not guilty.

“Mr. Harris has mourned the death of his wife since her passing and these charges are devastating to him and the entire family,” he said. “Mr. Harris has been fully cooperative throughout this very long, five year investigation and looks forward to taking advantage of every opportunity to defend against these allegations.”

It didn’t take long for police to grow suspicious of Harris. He had claimed Christina was battling a cold, but her mother had spent all day with her the Sunday before she was found dead, and told police she seemed perfectly healthy and “in good spirits.” She said the couple had a rocky relationship — and in a matter of days, Harris’s own family members came to police to explain why.

On Oct. 1, Harris’s sister and brother told Davison police that Harris had made comments in the past about “getting rid of Christina.” They thought he was seeing other women. They were right, Leyton said on Tuesday.

On Harris’s phone, they found nearly 5,900 text messages to a woman from Providence, R.I., plus emails and pictures sent to numerous other women, Leyton said. Nine days after Christina died, he bought a plane ticket to go visit the woman in Providence. And shortly after that, police learned from Harris’s neighbor that a woman and her daughter moved in with him in the home where his wife had died.

The neighbor told them about the cereal, too. Soon, they learned she wasn’t the only one to hear Harris’s mysterious story about the breakfast food. He told at least three co-workers, explaining how he had to carry her to bed after she fell out of her chair.

One co-worker asked him why he didn’t call an ambulance or get help — but Harris didn’t respond, Leyton said.

The stories from co-workers and friends kept getting worse, the county prosecutor said. Over lunch one day, a friend remembered Harris said he “just needed to get rid of Christina.” She asked him, why not just get a divorce? He didn’t want to lose his kids or deal with child support or alimony, Harris allegedly told her. At least three co-workers could also remember Harris telling them he “wished Christina was dead,” Leyton said.

To some of them, he revealed how he planned to make it happen.

From one co-worker, he asked for Xanax pills. Harris got five of them — only to come back to his co-worker to say he put them in his wife’s water. She stopped drinking it because she thought it tasted funny. So now Harris wanted to know, “Well, what pills are tasteless?” Leyton said.

He consulted another employee at work, seeking the odorless and tasteless pills. His questions got more specific: “What pills would knock Christina out so she would not feel anything?"

Until finally, growing impatient, Harris allegedly asked his co-worker if he could hire him for $5,000 to kill Christina himself. His other hit man had fallen through, Harris said, according to Leyton. The ex-con he hired was caught by police spying on Christina, and because he was found with a gun, the hit man was returned to prison, Harris allegedly said. (Leyton didn’t say whether police independently confirmed the story.)

But the co-worker apparently refused the offer. His options exhausted, Harris took matters into his own hands, Leyton said.

“We believe Jason Harris murdered his wife,” Leyton said. “We believe he put heroin into her cereal and milk the night that she died after getting it from someone, thinking it would be tasteless and odorless, much like he had asked his co-workers multiple times.”

Leyton said prosecutors believe he killed Christina after she discovered the text messages to the Rhode Island woman, then collected $120,000 in life insurance money once her death was ruled accidental by the coroner and immediately began a new life with the other woman.

It’s unclear why it took so long to complete the investigation; Leyton said the breast milk was tested in 2016. He said that he would never “arbitrarily charge anyone with any crime,” and thanked Christina’s parents for their patience. “I know this has been a long time coming,” he said.

Christina’s parents attended the news conference as Leyton revealed the details of the case, although they declined to talk to local reporters.

In an obituary for her in 2014, her family said she loved spending time with her children, swimming, crafting and having family game nights. Harris had asked that, in lieu of flowers, mourners offer donations to the family, made payable to him.