The state formally withdrew its charges against Willis in a motion to dismiss Wednesday morning, according to 7th Judicial District Attorney Clint Wellborn.

"In short ... the District Attorney's Office cannot foresee a circumstance where any reasonable jury would conclude the defendant, Diana Willis, was anything other than insane at the time of the commission of the offense," according to the motion.

Wellborn announced the dismissal of the charges at a brief news conference in Estancia.

Willis had been charged with abandonment or abuse of a child resulting in death. Her son, Richie Brown, was found dead from hypothermia Sept. 26, 2007, in a field south of Encino after a 36-hour search.

The then-25-year-old Oregon woman was driving through New Mexico from California, and told investigators she removed both her and her son's clothes and fled the car to protect her son and herself from spiders. Willis fell asleep and when she discovered Richie was missing, went to Encino for help.

Ray Twohig, Willis' attorney, commended the decision in a news release Wednesday, saying that Wellborn's action is "a shining example to other prosecutors who face difficult decisions about filing or dismissing criminal charges."

"Diana's mental illness was not known to her before this happened," Twohig said in his statement. "She has endured the suffering no mother should face, including a lengthy criminal prosecution. Now, at long last, though she will always grieve the loss of her son, she now has her freedom."

Two forensic psychologists, Samuel Roll, hired by the defense, and Mick Jespen examined Willis separately and both determined Willis suffered from paranoid schizophrenia, which "compelled her to a course of action that resulted in the death of her child," according to the motion.

According to a September 2009 report from Roll, both Willis' parents were hospitalized for schizophrenia, and her siblings had been diagnosed with the same disorder.

"The combination of strong genetic predisposing and a terrorizing combination of environmental factors doomed Ms. Willis' fate," Roll wrote. "The sad irony is that Richie died, not because his mother was neglecting him, but rather that he died because his mother, in her own psychotic way, was protecting him."

Jespen had similar conclusions in his Feb. 9 report.

"Because of the symptoms of her mental illness (hallucinations and delusions), I don't think Ms. Willis was capable of understanding the true nature of her behaviors or their possible consequences to her baby or herself," the report states. "Nor do I think she could stop herself from following her deluded course of action in attempt to save herself and her baby from her hallucinated spider attack. I believe there is plenty of documented information about Diana Willis' mental state ... to support a finding of criminal insanity."

Willis had been found competent to stand trial in 2008, but Wellborn said Wednesday that Willis clearly had mental problems at the time of her son's death.

These findings prompted the district attorney to file the motion to dismiss all charges.

Willis, who Wellborn says has been receiving psychological treatment for her mental illness, has been working in Albuquerque. Her family is in Oregon, Deputy District Attorney Stacey Ward said, and Richie's father lived in California, where Willis had been traveling from at the time of her son's death.

The District Attorney's Office is not sure if or when Willis will be leaving New Mexico.

The search for Willis and her young son began around 2:30 a.m. on Sept. 25, 2007, when the Torrance County Sheriff's Department was notified by a truck driver that he had seen a woman walking naked on U.S. 60 near Encino, holding a child in her arms. Another reported sighting of the woman came about an hour later.

Deputies located Willis about 8:30 a.m. that day, but the child was not with her. Willis was taken to Anna Kaseman Hospital in Albuquerque, where she was committed. In an interview with deputies, Willis said she and her baby left the car after she drove over a large spider on the road.

She said she believed spiders were "attaching themselves" to her vehicle. Willis pulled over and picked up her son. She took off her clothes "along with her infant son's clothing to keep those spiders from continuing to bite her and laying eggs in their clothing," according to court records. After petting a horse and lying down in a field, she could not find her son.

Richie Willis' body was found with the help of more than 50 searchers from several police and fire departments.