Almost four months after 17-year-old Jake Evans calmly confessed to a 911 operator that he had just murdered his mother and sister at their Aledo home -- "It's weird," he said. "I wasn't even angry with them. It just kind of happened." -- the teen's written account of what happened on the night of October 3 has been introduced at his trial.

He had been inspired, he wrote, by Rob Zombie's 2007 remake of Halloween, particularly the part where a 10-year-old Michael Myers calmly kills several people. He watched it three times.

"While watching it, I was amazed at how at ease the boy was during the murders and how little remorse he had," Evans wrote, according to NBC 5. "Afterward, I was thinking to myself it would be the same for me when I kill someone."

Then, as he watched the October 3 presidential debate with his mother, Jami, and 15-year-old sister, Mallory, he began thinking about how he would kill them. He retrieved a knife, then thought better of it and grabbed the .22 revolver he'd stolen from his grandfather. That way, there would be less pain.

The next hour he spent pacing around the house "thinking how life will never be the same and how I would never see them again," then knocked on his sister Mallory's door and said she was needed by their mother.

"She came out and out of the corner of her eye she saw me pointing the gun at her," he said. "She thought I was joking and told me that I was freaking her out. I shot her in the back and then the head."

He found his mother in the study and shot her three times, then returned to his room.

"As I emptied the shells on my bed, I heard noizes (sic) and realized that Mallory was still alive," he said. "While I loaded the gun back up, I was shouting that I was sorry and then ran as fast as I could to kill her. I made sure my mom was dead and shot her again in the head."

Then, he called 911.

"I know now though that I'm done with killing," his written confession concludes. "It's the most dreadful and terrifying thing I will ever experience. And what happened last night will haunt me forever."