NASHUA, N.H. — The murder defendant in a deadly New Hampshire home invasion and machete attack testified Monday he fantasized about torturing and killing his mother from age 14 on because she abused him.

Christopher Gribble, 21, surprised courtroom observers by taking the witness stand on the heels of his mother’s testimony. He told jurors he was agitated because his mother, Tamara Gribble, had lied when she denied abusing him.

Christopher Gribble has admitted stabbing Kimberly Cates to death and trying to kill her 11-year-old daughter, Jaimie, in their Mont Vernon home in October 2009. He is now trying to convince the jury he is not guilty by reason of insanity.

Two defense experts testified Monday that he had antisocial personality traits but was not insane.

Gribble said he fantasized about taking his mother into the woods and cutting off little pieces of her “bit by bit, listening to her scream.” He also said he thought about pouring boiling water “over sensitive parts of her,” bending her limbs out of joint and sprinkling her with sugar so the crows would come and pluck at her.

“Hey, if I’m going to kill her, why not make her pay?” he said with a shrug.

Tamara Gribble testified that she spanked her son with a wooden spoon one time when he was 5 and wet himself. She said she hit him hard enough to break the spoon and was “devastated” afterward by her rage. She kept the broken spoon in her bureau as a reminder of her regret, she testified.

She denied other things her son had told mental health counselors, including that he was forced to vacuum the house at age 6.

She wept when she testified about the spanking and again when prosecutor Jeffery Strelzin asked about the attacks and whether she now knows where Gribble was the night of Oct. 3-4, 2009.

“Yes, I do,” she sobbed. “I’m sorry.”

She testified he came home around 11 a.m. Oct. 4, just hours after the predawn attacks, and ate breakfast with her at the table. After his arrest she thought the police had made a mistake.

“I said he couldn’t be this calm and normal,” Tamara Gribble testified. “I couldn’t believe anyone could take a human life and not be distressed to their core.”

Christopher Gribble said that, as a child and young teen, his mother regularly would pin him to the couch and told him not to make any noise while she popped acne and other sores on his back and legs and pulled hairs from his head.

“If I cried, I got smacked,” he said. “She called it the owie-check.”

Gribble’s two-hour testimony, which resumes Tuesday, was at times rambling and contradictory.

He told the jurors at length about weekly sessions playing the computer role-playing game, “Dungeons and Dragons.”

“I found I had an incredible ability for strategical and tactical thinking,” he bragged.

Gribble said he couldn’t believe his father was unaware his wife abused him but also said his father held him down for one or two of the “owie-check” sessions.

He described his mother as being two-faced and said the two did not have a good relationship. “In public, in here, she’s sweet and charming,” he said. “She’s good at it. She can pull it off. I learned everything from her.”

Prosecutors say Steven Spader, who was convicted of first-degree murder in November, wielded a machete and Gribble a knife in the attacks on the mother and daughter.

A medical examiner testified during Spader’s trial that Kimberly Cates was alive while all 32 blows from the knife and machete ripped through her body.