"He said that he got a beer and went and got all the medications in the house and fed them into this beer," she testified. "He helped her sit up and drink it, and watched her stop breathing."
MacNeill's sister eventually came into the house, sought medical help and revived their mother.
Walthall said she asked him later if he ever regretted the incident.
"He said he regretted that there wasn't more medication in the house," she testified.
In later years, though Walthall could not recall if he ever told her when specifically, she testified that he told her he killed his brother. MacNeill allegedly said his brother wasn't suicidal, but often cut his wrists for attention. Once, while MacNeill was visiting in New Jersey, his brother called him and told him that he had hurt himself, so MacNeill went to his mother's home, into the bathroom, and found his brother with his wrists cut, lying in a bathtub.
MacNeill held him underwater until he drowned, she said.
Walthall said she once asked him if he was ever worried that he would get caught.
"He said that it was not unusual for a cutter to drown because they lose enough blood that they don't have the strength to stay above water," she said.
MacNeill, a 56-year-old Pleasant Grove doctor, is accused of killing his wife on April 11, 2007, in order to free himself to continue an affair with another woman named Gypsy Willis.
MacNeill allegedly gave 50-year-old Michele MacNeill a deadly mixture of prescription drugs after she came home to recover from cosmetic surgery in April 2007.
Walthall was one of seven witnesses who testified Thursday, the second day of MacNeill's multi-day preliminary hearing. After the hearing ends next week, Judge Samuel McVey will decide if there is enough evidence to order MacNeill to stand trial on charges of first-degree felony murder and obstruction of justice, a second-degree felony.
From the beginning of Walthall's testimony, MacNeill's defense attorneys, Randy Spencer and Susanne Gustin, objected to much of what the woman revealed. Walthall is diagnosed with dissociative identity disorder, which Gustin said she felt affected the woman's ability to discern fact from fantasy.
But Utah County prosecutor Chad Grunander said that although Walthall is mentally ill, she is high-functioning and has the ability to decipher truth from a lie, and has a clear memory.
"Despite her mental illness, she has been very candid and open," he said outside court.
Earlier Thursday, MacNeill's neighbor, Doug Daniels, testified helping to remove a lifeless Michele MacNeill from bathtub where she was found and assisting in CPR efforts.
"[MacNeill's] demeanor, it would change, which we thought was a little bit different," Daniels testified. "He was very analytical sometimes, telling us what to do, and then would tell us to stop … and then he would have a bit of an outburst over the situation, I guess. He would kind of stop everything, and he would say, 'Why? Over a stupid surgery!' and then continue."
At that time, Daniels had been giving the woman chest compressions while MacNeill gave him instructions and conducted mouth-to-mouth with his wife. But Daniels said Thursday that he never saw the woman's chest rise or fall, a standard of proper CPR.
When asked by Spencer whether he may not have remembered if her chest rose and fell, Daniels said he was sure of it.
"It's not a matter of recalling," Daniels said. "I didn't see her chest rise."
Two Pleasant Grove police officers who responded to Martin MacNeill's 911 call, were struck by the man's anger, according to testimony.
"He was very angry," Ray Ormond, one of the officers, recalled Thursday on the witness stand. "He was very angry with us. … It was uncomfortable, honestly, to have him coming back and forward into the room yelling at us."
Ormond said the officers eventually moved Michele MacNeill from the bathroom into a bedroom and continued CPR. The woman, who was abnormally cold to the touch, began regaining a bit of color as the CPR efforts starting circulating her blood once again. Eventually, she coughed up what Ormond thought was three to four cups of water, but she could never be revived.
Dr. Scott VanWagoner, an emergency physician at American Fork Hospital, where Michele MacNeill's body was taken, also testified Thursday that MacNeill's behavior was extremely odd.
"One of the oddest comments, to the point of being bizarre, is he offered me $10,000 to stop my resuscitation efforts," he said.
The state medical examiner has never ruled Michele MacNeill's death a homicide. After an autopsy in 2007, her manner of death was ruled "natural," the result of "chronic hypertension and myocarditis, which are capable of causing acute unexpected arrhythmia and sudden death."
But investigators say Martin called the medical examiner multiple times and gave misleading information. In 2010, in a new investigative report, Chief Medical Examiner Todd Grey changed the cause of death to the combined effects of heart disease and drug toxicity. The manner of death was changed to "undetermined."
In recent years, other experts have also reviewed the case. A University of Utah professor of pharmacology and toxicology said he believed Michele MacNeill had taken a potentially lethal dose of medication. A medical examiner in Florida determined the immediate cause of death was drowning and that, contrary to the Utah medical examiner's findings, there was no evidence of acute or active myocarditis.