A woman accused of killing her autistic daughter testified Friday that she attempted to suffocate the 3-year-old with a pillow three days before she succeeded with a plastic garbage bag.

Karen McCarron said she couldn't go through with it using the pillow. When prosecutor Kevin Johnson asked her how long she held the bag over the toddler's head soon after, she replied about two minutes — until little Katie stopped struggling.

In a videotaped confession played in court Thursday, McCarron said she began having thoughts of hurting her daughter a year before the May 2006 slaying but put them out of her mind. On the day of the killing, though, the thoughts were stronger than ever.

"They were so intense," McCarron said.

McCarron, 39, has pleaded not guilty by reason of insanity to murder, obstructing justice and concealment of a homicidal death. She was found mentally fit to stand trial, but a medical expert hired by her attorneys has said she was insane at the time of the killing.

The trial resumes Monday.

McCarron, a former pathologist, testified she felt responsible for Katie's autism because she allowed the child to get vaccinated. Some people believe autism is caused by a mercury-containing preservative once used in childhood vaccines.

It "brought me a great deal of guilt," she said.

Using a plastic bag and the prosecutor's arm, McCarron demonstrated for jurors in Tazewell County Circuit Court how she placed a bag over her daughter's head and pushed her to her knees, the (Peoria) Journal Star and the Pekin Daily Times reported.

"Were you able to see her face as she fell to the floor?" Johnson asked.

"Yes. I could see her face through the trash bag," McCarron answered.

McCarron said she listened for a heartbeat after Katie stopped struggling.

"I just put my ear to her chest," McCarron said. "I heard one, then I heard nothing."

The child had scratch marks on her head and bite marks were found inside her mouth and on the bag as she apparently tried to free herself, according to other testimony.

The taped confession was made while McCarron was hospitalized after attempting suicide, investigators said. Wearing a hospital gown, she appears sitting on a bed next to her husband, Paul McCarron.

Karen McCarron said she killed her child hoping to "fix her" and give her peace in heaven.

"Maybe I could fix her this way, and in heaven she would be complete," she said on the tape.

Karen McCarron said on the videotape that she took her daughter's body back to her own house and put her in bed. She then went to the store, bought ice cream and returned to her mother's home to get the garbage bag because, "if things get bad, their house would be searched."

Interviewers asked McCarron if she knew what she did was criminally wrong.

"I have enough education to know that," she answered.

McCarron told police she felt like a failure because of the child's autism and was sad and hurt because the child couldn't interact with her very well.

"I loved Katie very much, but I hated the autism so, so much," McCarron said. "I hated what it was doing to her. ... I just wanted autism out of my life."