A Snohomish County Superior Court jury deliberated less than a day before determining that Opel, 39, arranged the killing of Jerry D. Heimann, who had hired her to care for his aging mother.
Heimann, 64, was beaten and stabbed to death in April 2001 by a group of teenagers - including Opel's eldest daughter Heather, now 15. All of the teens have pleaded guilty or been convicted in his death.
The sentencing phase of Barbara Opel's trial was to begin Thursday, her attorney, Peter Mazzone said, declining to comment further.
Opel could become the first woman on death row in Washington state if jurors decide she should get the death penalty instead of life in prison, the only options for an aggravated-murder conviction.
Prosecutors told jurors Opel orchestrated the murder, promising the teens money and gifts for carrying it out, so she could steal $40,000 Heimann had made from the sale of a house.
Defense lawyers contended Heimann was killed in "a violent frenzy concocted by the teenagers themselves."
Opel moved in with Heimann in late 2000 for reduced rent in exchange for cooking, other chores and caring for his 89-year-old mother, who had Alzheimer's disease.
Opel testified over two days in her 2½-week trial, saying Heimann had become increasingly abusive to her and her children and she wanted to teach him a lesson.
The plan, she said, was to have Heather Opel's boyfriend, Jeff Grote, 17, recruit two seventh-graders to help beat up Heimann, a retired Boeing worker with terminal cancer. Heather and her friend, Marriam Oliver, then 14, also were involved in the attack.
Heimann's mother was left alone in the house after her son's slaying. Relatives arriving from out of state found her at the house and called police.
Investigators later found Heimann's body in a shallow, rural grave with help from one of Opel's two younger children.
Three of the teens testified that Opel had encouraged them to kill Heimann.
Opel acknowledged that she often discussed Heimann, saying she wished he were dead. She also said she tried to hide the man's body to protect her daughter.
The day of the attack, prosecutors allege, Barbara Opel waited in the basement with her two other children - an 11-year-old boy and a weeping 7-year-old girl - and shouted encouragement to the teens assaulting Heimann.
"Barbara was in charge. She was the supervisor of this whole grisly scenario," Deputy Prosecutor Chris Dickinson said in closing arguments Monday.
Heimann's body was found in a shallow rural grave April 21, 2001, eight days after the killing. Opel initially claimed Heimann was out of town, but her 11-year-old told officers what had happened and led them to the body.
Heather Opel and Marriam D. Oliver, 14 at the time of the attack, were sentenced to 22 years in prison last year after pleading guilty to first-degree murder. They each have appealed the decision to try them as adults, and could see their sentences reduced if those appeals are successful.
Grote, at 17 the oldest involved, pleaded guilty to first-degree murder and likely faces a 50-year sentence.
Kyle Boston of Arlington, 14 at the time of the attack, pleaded guilty to second-degree murder in adult court and his cousin from Marysville, then 13, was convicted of first- and second-degree murder in juvenile court. The juvenile can be held no longer than age 21.
Boston could face a sentencing range of 10 to 18 years. Sentencing for Boston and Grote was delayed pending their testimony at Opel's trial.
Boston received $220 cash for his participation, his cousin said. The 13-year-old said he got about $100, which he used to buy a sweatsuit.