A Kila man on trial for savagely beating his wife's lover last year testified Tuesday in his own defense.

Robert Reynolds Derby III, 35, told the jury he remembers walking in on his naked wife in bed with another man - and then he remembers nothing else until dialing 911 to report the beating.

"I just lost it… completely lost it," Derby said. "When I saw her I just completely lost control… I don't know how to explain it."

Using a strategy similar to temporary insanity, defense attorney Thane Johnson is arguing that the attack was an "involuntary act" committed after his client 'snapped."

During questioning Tuesday, Johnson held up pictures of the victim's injuries and Derby's own blood-covered hands. Johnson asked his client how the images made him feel.

"Terrible," replied Derby, breaking down. "Can't believe that's me."

But Flathead District Judge Katherine R. Curtis ruled that Johnson's question allowed prosecutors to introduce Derby's previous arrest for assault.

On cross examination, Flathead County Attorney Ed Corrigan portrayed the attack as conscious and consistent with Derby's history of violence.

According to testimony, sheriff's deputies responding to a home on Spring Hill Drive in Kila just before 11:30 p.m. on March 3, 2008, found the victim with bruised ribs, a broken jaw and an injured eye.

The emergency room doctor who treated the 29-year-old man injured in the attack testified Tuesday it appeared Derby stuck his thumb into the alleged victim's eye socket and "tried to pry his eye out and did."

Also Tuesday, Derby's daughter - who was in the home with her two sisters when the attack occurred - told the court her father "tried to be affectionate" with her mother but that her mother "didn't want anything to do with it."

She also testified that, after the attack, Derby brought her and her sisters into the room and told them: "This is what happens when you lie."

But Derby's mental break after discovering the alleged victim in the bedroom was aggravated by the fact that his wife told led him to believe she wanted to reconcile while the victim had told him the affair was over, Johnson argued.

Derby pleaded not guilty in March to aggravated assault, criminal endangerment, misdemeanor partner assault, and misdemeanor endangering the welfare of children.

If convicted on all charges, Derby could face a maximum sentence of more than 31 years in prison and a $101,000 fine. His trial is scheduled to last through Thursday.

Reporter Nicholas Ledden can be reached at 758-4441 or by e-mail at nledden@dailyinterlake.com