Aug. 27, 2012— -- The daughters of a doctor now facing murder charges in the death of his wife say they always knew their father had a plan to kill their mother and are "happy" he has finally been arrested.
Police arrested Martin MacNeill, 56, on Friday and booked him into the Utah County Jail for first degree murder. The doctor and former Mormon Sunday school teacher served three years in a Texas federal prison for fraud and was released in July.
An initial autopsy report stated that Michele MacNeill, 50, had died of natural causes in April 2007, but authorities now believe Martin MacNeill drugged and drowned his wife, who was found unconscious in the bathtub.
MacNeill's daughter, Alexis Somers, had long fought for police to reopen the case, believing her father was responsible for her mother's death. Somers and her sister, Rachel MacNeill, had led the charge against the man they once called dad.
"We know he's guilty. We know he'll harm again. If he's let out he will come after us," said Rachel MacNeill. Somers said she was "so happy" and had waited "so long" for her father to be held accountable.
"It's horrible to be happy about the arrest of your father, but finally he is being held accountable for murdering my mother," she said.
It's a twisted family tale that began when Martin MacNeill, a father of seven, turned 50. His daughters said he became obsessed with his looks and started to tan and exercise. Their mother began to suspect an affair. Then, MacNeill focused on his wife's looks, insisting she get a face-lift.
"He had a plan to murder my mother, and this was just part of his plan," said Somers.
While caring for her mother after the surgery, Somers said she heard a bombshell just days before her mother died. "A few days before her death, I was helping her wash her hair and she turned to me and said, 'Alex if anything happens to me make sure it was not your father,'" said Somers.
On the day Michele MacNeill died, Martin MacNeill had arrived home after picking up his then 6-year-old daughter from school. They found Michele in the bathtub.
In a series of screaming 911 calls, Martin McNeill hung up on the operator three times in five minutes. During that time, prosecutors say he removed his wife's pants, lied to the dispatcher about performing CPR and gave the wrong address of his residence, further delaying emergency responders.
Michele MacNeill's autopsy initially concluded that she died of natural causes. Later, investigators changed the cause of death to "Undetermined," saying new information raised "suspicion," including the possibility that the combination of drugs in her body could have killed her and she may have been forced to take them.
Prosecutors now believe MacNeill gave his wife a dangerous combination of valium, Percocet and Ambien.
A search warrant filed last year lays out the seemingly perfect motive: MacNeill's alleged affair with Gypsy Willis, who moved into the family's home as a "nanny" two weeks after Michele's death. The warrant alleges that MacNeill "intentionally overdosed" his wife after she had plastic surgery because she approached him about the alleged affair. Somers vividly recalls the day her father called to inform her of her mother's death.
"When my father called I knew he'd killed her," Somers told ABC News. "I just started screaming he killed her. I knew it."
MacNeill's attorney, Randy Spencer, said MacNeill "continues to adamantly deny that he killed his wife, and is confident the truth will set him free."
"My father planned and orchestrated my mother's death, and he thought he could get away with it," said Somers.
ABC News' Alyssa Newcomb contributed to this report.