The court ruled the guilty verdicts against Kevin Shannon Jones cannot stand because evidence of past crimes was improperly admitted and could have unfairly influenced the jury, The Register-Guard newspaper reported Saturday.
The state Justice Department must decide whether to seek further appeals or send the case back to Lane County for another trial.
The case already has been heard by the Oregon Supreme Court, after the appeals court initially upheld the convictions. The high court returned the case to the appeals court for reconsideration because of a new ruling in a similar case.
The jury convicted Jones in July 2009 and he was sentenced to 56 years in prison. He was 26 at the time.
The convictions included felony assault charges for burning the woman with a lighter, hitting her with barbecue tongs and a crescent wrench, cutting her with a knife, putting hot sauce in her eyes, pulling a tooth, holding a machete to her throat, and shaving her hair and eyebrows to make her unattractive to other men.
The woman was covered in scars and bruises when she went to a hospital to give birth, a prosecutor told the jury in 2009.
During his closing argument, defense attorney Chris Hansen said the woman was injured by someone else.
Hansen cited testimony by workers at a local center for homeless people who did not remember seeing injuries on the woman and who described Jones treating the victim lovingly after she went into labor. Hansen also said the victim engaged in risky behavior, such as methamphetamine use and sexual activity with other men.
The appeals court found that testimony by one of Jones' former girlfriends was not properly admitted. The woman testified that in 2007 Jones had held her captive in the sleeper cab of a freight truck he was driving and for several days beat, choked and threatened to kill her.
"In sum, the improperly admitted evidence was highly inflammatory and easily could have been improperly used by the jury as demonstrating defendant's propensity to commit outrageous assaults against domestic partners," the court found. "The admission of that evidence was not harmless."