In closing arguments on Friday, the court heard audio from Mr Mullis' emergency 911 phone call which he made when he allegedly discovered her body. He could be heard breathing heavily and whispering words which the prosecution said included: "go to hell you cheating whore". Prosecutors alleged Mr Mullis was irate over his wife's affair.
Mr Mullis said he didn't know what he had said in the recording but that it wasn't those words.
The court also heard that Mr Mullis' iPad had been used to research punishments for cheating spouses.
On Thursday, Mr Mullis testified that he didn't know who used his iPad to search terms that included: "killing unfaithful women", "organs in the body", "what happens to cheaters in history" and "what happened to cheating spouses in historic Aztec tribes". He said his wife and others knew his password.
A state investigator testified that Mullis never denied killing his wife. But Mr Mullis said investigators wanted him "to confess to something I didn't do".
Ms Mullis loved hunting, fishing and spending time outdoors and had left her job as a registered nurse so that she could help out in the barn, her brother testified in court on Tuesday. But Mr Mullis was allegedly so controlling that Ms Mullis' friends called her "POT," — short for "Prisoner of Todd". As soon as all their crops were out of the field, she told her brother in August 2018, she planned on leaving him and filing for divorce but had expressed fear Mr Mullis would "flip out".
A prosecutor said Mr Mullis was angry that his wife wanted to leave their 14-year-marriage and fearful that he'd lose their farm and millions of dollars if she divorced him.
"Amy Mullis would be alive today if it weren't for the actions of her husband," State Prosecutor Marie Hughes said.
Mr Mullis' lawyer, Jake Feuerhelm, argued that while there was no doubt Ms Mullis had been "viciously and deliberately murdered," there was plenty of reason to question whether his client was the person who killed her.
The man Ms Mullis was having an affair with, Jerry Frasher, worked on the couple's farm as a field manager. He testified that Ms Mullis told him last year she was deathly afraid of her husband.
The Telegraph Herald reported that Mr Frasher said he started a sexual relationship with Ms Mullis in late May or early June last year.
"I know she wasn't happy," Mr Frasher testified. "She said she felt like a slave or a hostage around there. She said she was wanting (to leave Mr Mullis) … she said if he ever found out (about the affair,) she would disappear."
Mr Mullis confronted him in July 2018 after a phone bill showed more than 100 instances of Frasher and Amy texting, Mr Frasher said.
"I said it was about other stuff, like showing pigs," he said.
Mr Mullis called Mr Frasher's wife asking questions about the text messages, and their discussion appeared to satisfy him, according to Mr Frasher.
"Two days later, he called us both back and apologised," he continued.
"He asked us to quit texting, and we did."
Mr Frasher said he told Ms Mullis: "We need to slow down".
During cross-examination Mr Frasher said he continued to provide professional services to the Mullis farm until Ms Mullis' death. He said Mr Mullis never showed any animosity toward him.
The court heard that Ms Mullis had expressed fears to several close friends that Mr Mullis would kill her and "throw her to the pigs" if he learned about her infidelity.
Forensic pathologist Kelly Kruse, who performed an autopsy on Ms Mullis' body, testified that the victim was impaled by a corn rake "at least twice, possibly three times".
"The manner of death was homicide," Dr Kruse said.
The jury retired to deliberate on Friday afternoon local time.
Mr Mullis faces a potential life sentence in prison if convicted.
