"He's a sexual predator," Somers said after the verdict was read. "There's some justice. … The jury once again saw the truth."
A previous Utah County jury convicted MacNeill last year of murdering his wife by drugging her and drowning her in a bathtub at their Pleasant Grove home.
After Thursday's verdict, defense attorney Randall Spencer said MacNeill was "very disappointed" but "not terribly surprised." He said MacNeill will appeal. "There was lots of reasonable doubt in this case," Spencer added.
Just before closing arguments were delivered Thursday, Somers told reporters she was not MacNeill's only sexual-abuse victim, but did not elaborate further. She said she wanted the case to go to trial and "felt it would send a wrong message" if it had ended in a plea deal.
"As a victim of sexual abuse, I felt it a duty to come forward and seek justice for these crimes," Somers said. "Regardless of the outcome, I think I will sleep a little better tonight knowing I've done everything in my power to protect my family, protect my little sisters and others from my father, who is a murderer and a sexual predator."
During closing arguments, Spencer told the jury that Somers had a motive to misrepresent or slant her testimony: to get custody of her younger sisters after her mother died.
Deputy Utah County Attorney David Sturgill did not disagree that Somers had a motive but said that it doesn't mean she was untruthful.
"In her mind, she decided, 'I have to come forward,' " Sturgill said. " 'The reason I am doing it is because I am concerned about the safety of my younger sisters.' So, yeah, she did have something to gain by coming forward. That doesn't mean she lied about it. She came forward to protect those kids."
Somers testified that she threatened to go to the police about the alleged abuse unless MacNeill gave her custody of his young children.
"He said, 'You can try to fight me, but I'm going to destroy you,' " she testified.
She said she responded, "I'll do whatever it takes [to get custody]. But I won't lie."
Somers said she eventually contacted Pleasant Grove police and child protective services.
Under cross-examination, Spencer attempted to poke holes in the woman's testimony, questioning inconsistent statements and why she waited several months to report the incident.
The alleged sexual abuse occurred May 23, 2007, about five weeks after the death of MacNeill's wife, 50-year-old Michele MacNeill.
Somers testified that after she awoke at the home to find Martin MacNeill rubbing her buttocks, and licking and kissing one of her hands, the man said: "Oh, oh, I'm sorry, I'm sorry. I thought you were your mother."
Until Thursday, The Salt Lake Tribune has not identified Somers by name because she was an alleged sexual-assault victim.
MacNeill, 58, was found guilty of second-degree felony forcible sexual abuse.
The former doctor already faces life in prison, having been convicted in November of murder and obstructing justice in Michele MacNeill's April 2007 death. He has yet to be sentenced in the murder case.
In that case, 4th District Judge Derek Pullan is mulling a defense motion for a retrial. Spencer argues that a federal inmate lied on the stand about a possible early release he received in exchange for his testimony and that prosecutors did not disclose that a deal was in the works.
Pullan said earlier this week he will need about 60 days to look over the evidence before ruling.
The federal inmate testified during MacNeill's four-week trial that the defendant confessed to him that he drugged his wife, then drowned her in a bathtub at their Pleasant Grove home April 11, 2007.
Prosecutors said MacNeill killed his wife so he could continue an affair with another woman, Gypsy Willis.