Rather than continue an ugly custody dispute, Amy Lewis Oliver gave her 3-year-old son a lethal dose of medication, then cut herself with a razor blade and was lying on the bed with him to die when the father intervened, according to an arrest warrant.

Friday the State Attorney's Office announced she pleaded guilty to second-degree murder in the 2020 death of their young son, Henry Prisby, in Jacksonville Beach. Per terms of the plea agreement, Oliver will be sentenced to 40 years in prison as opposed to life for a first-degree conviction.

Court records show she also pleaded guilty to aggravated assault on an emergency medical care worker. Oliver, 48, of Green Cove Springs was initially charged with the latter offense and possession of a controlled substance. She was later charged with first-degree premeditated murder, culpable negligence manslaughter of a child, aggravated child abuse and child neglect.

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The boy's father called 911 from his home in The Sanctuary community of Jacksonville Beach that Oct. 27 saying Henry was not breathing and that Oliver “tried to kill” their son, according to the State Attorney's Office. Rescue personnel found the boy unresponsive in the main bedroom and Oliver barricaded in a bathroom.

Once the door was broken down, Oliver attacked first responders with a syringe before being detained and hospitalized. She was covered in blood from self-inflicted wounds, the State Attorney's Office said.

The father said he and Oliver shared custody of the child and were not married, according to the arrest warrant.

The investigation revealed Oliver was there to pick up the child and asked to take a nap before heading back to Green Cove Springs, so Henry’s father obliged. Later when he went to check on them, he found the bedroom door locked, the warrant said.

He knocked, and Oliver said to hold on. Then he received concerning text messages from Oliver and forced his way in, the warrant said. He found "a large amount of blood on the bed" and the unconscious body of their son. Oliver wouldn't come out of the bathroom.

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She had also sent scheduled emails to others about her and Henry’s demise, according to the State Attorney's Office.

Henry died from a lethal level of a sedative that his mother was prescribed and administered to him, the medical examiner ruled. 

Prior to Friday's plea, Oliver had sought an insanity defense. Last month's filing says she suffers from a "constellation of mental infirmities, diseases and defects, including depression, anxiety, premenstrual dysphoric disorder and other undiagnosed and unspecified mental disorders," news partner First Coast News reported. 

"Because of these conditions, she did not know what she was doing was wrong," her defense team said.