After taking her 6-year-old son for ice cream, Jillian McCabe parked her red Volkswagen Cabriolet near one end of the Yaquina Bay Bridge, grabbed the boy's hand and walked with him toward the middle.

It was after 6 p.m. on Nov. 3, 2014, with heavy traffic on Newport's signature arch span. McCabe had left so hastily from home that she neglected to bring along a coat for the kindergartner.

When the mother and son were near the center of the bridge, McCabe lifted London in her arms, then put him back down. She started back to her car by herself.

She soon turned around. She lifted her son again, said "sorry" and pushed him over the edge. McCabe didn't look back as she walked away and heard a splash.

Once back at her car, McCabe called 911 and told emergency dispatchers that she had just thrown her son off the bridge. She claimed voices told her to do it and that she should jump as well.

On Tuesday, Lincoln County District Attorney Michelle Branam said McCabe, 36, was "rightfully" sentenced to life in prison for the murder of her son. McCabe won't be eligible for parole for 25 years.

During a news conference that included McCabe's ex-husband and his parents, the prosecutor detailed how the mother spent more than a month researching ways to kill her only son and get away with it.

"Hearing voices," "child off bridge" and "insanity defense" were among the many search terms discovered by investigators on McCabe's phone and computer. Journal entries written by McCabe also confirmed her intent to kill her son, Branam said.

"Everyone hopes this can be explained by way of mental illness so we don't have to leave open the possibility that a mother could plan to so horrifically murder their child," Branam said. "But it appears from the evidence we have in this case that this was exactly what happened."

London McCabe's autism made him the "perfect victim" for his mother, Branam said. He trusted her completely and likely didn't struggle even as she hoisted him over the bridge railing, the prosecutor said.

The fall from the bridge -- about 133 feet to the water -- broke several of the boy's bones, Branam said. He drowned in the bay. Searchers found his body hours later near docks about a mile from the bridge.

McCabe, a stay-at-home mother, was scared that her lifestyle would change after her husband was diagnosed with multiple sclerosis and could no longer work, Branam said. She concocted the plan to rid herself of responsibility for the boy and live at the Oregon State Hospital.

Jillian McCabe pleaded guilty Monday to murder during a hearing in Lincoln County Circuit Court.

She has appeared happy in jail over the past year awaiting trial, Branum said. McCabe didn't mention her son's name for months and cheerfully discussed the books she'd read while behind bars, showing no remorse, the prosecutor said.

Jillian and Matt McCabe married in October 2005 and London was born three years later. They lived in The Dalles, where Matt McCabe had a successful career working in information technology. He mostly took care of their son, Branum said.

In March 2011, London was diagnosed with autism. In November 2013, Matt McCabe was diagnosed with multiple sclerosis. He remained hospitalized until that January. He had to relearn how to walk, read and could no longer work.

Jillian McCabe voluntarily sought help at a mental health care center in February 2014 after she threatened suicide. She returned to her family, but was admitted again in April.

When she was released that same month, Matt McCabe's uncle and aunt offered to have Jillian McCabe live with them in Portland. Matt McCabe and London moved in with his parents in the Newport area.

Jillian McCabe sought help a third time at a mental health center after the aunt and uncle found a letter she wrote detailing plans to kill the couple's dog, bludgeon the aunt to death while the uncle was away and then burn down their home to destroy any evidence.

Each time she received mental health treatment, McCabe requested to go to the Oregon State Hospital and was disappointed each time when she was told she didn't have symptoms that warranted the transfer, Branam said.

McCabe went to live with her husband and son in September at his parents' home about eight miles from the Yaquina Bay Bridge.

She didn't allow her husband or his family to have access to her mental health records, Branam said. The family didn't allow her to be alone with London, but over time allowed an increased role in aiding in his development, such as helping potty-train the boy and getting him used to communicating with picture cards.

In October, McCabe searched "can you die from falling 133 feet into water?" She searched "Andrea Yates" 60 times on her phone, Branam said. Yates is a Texas woman found guilty by reason of insanity in 2006 after drowning her five children in a bathtub. McCabe also looked up the legal defenses of other people who have thrown children from bridges.

While her husband and mother-in-law were away from home on Nov. 3, McCabe told her father-in-law she was taking London to get some ice cream. He didn't suspect anything was amiss because they were allowing McCabe to be more independent.

After throwing the boy off the bridge, McCabe told her husband that she heard voices and saw demonic faces when she looked in the mirror, but Branam noted that McCabe intentionally hid any indication from her family that she considered harming the boy.

"When it suits her, Jillian was able to ignore the voices, for example, when they told her to jump off the bridge," Branam said. "She was only unable to fend them off when she was told to throw London off the bridge."

Reitha McCabe, Matt McCabe's mother, said the family thought Jillian McCabe's sentence was "fair and merciful," but "no amount of punishment can make up for the value of London's life."

Matt McCabe said the loss of his son has left a large void in his life. He said the sentencing of his now-ex-wife brings him no closure. She had a mental illness, he said, but he trusted mental health professionals when they told her she was "cured" and believed his son wasn't in danger.

"If you know someone with a mental issue, take it seriously," he said. "It's a matter of life and death."

He said he will miss his son forever.

-- Everton Bailey Jr.

ebailey@oregonian.com

503-221-8343; @EvertonBailey