Marietta, Georgia (CNN) Justin Ross Harris, who faces murder charges in his 1-year-old son's June 2014 hot car death, will not see a separate trial on allegations that he sexted with minors, a Cobb County, Georgia, judge ruled Monday.

While the prosecution said the sexting-related charges help establish motive, Harris' defense attorney, H. Maddox Kilgore, told Superior Court Judge Mary Staley that he didn't believe the charges that Harris sent minors sexually explicit material had anything to do with the allegations that he intentionally killed his son.

"Severance is warranted and, I believe, mandated in this case," he said. "How do sending these photos show disposition to killing a child?"

Harris left Cooper in a rear-facing car seat in the back of his Hyundai Tucson while he spent the day at work as a Web developer for Atlanta-based Home Depot. He normally dropped the boy off at day care.

The temperature topped 92 that day, which can make the heat inside a closed vehicle soar past 100 degrees quickly, and police testified during Harris' probable cause hearing that Cooper spent at least seven hours in the car.

Cobb County police Detective Phil Stoddard has taken the stand in the past to say that Harris was sexting minors while Cooper was in the car that day. At Monday's hearing on separating the charges, he testified that Harris commented on the morning of Cooper's death, via the anonymous messaging app, Whisper, "I miss having time to myself and going out with friends."

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Harris also wrote on Whisper that he hated being married with kids, Stoddard said, in an attempt to establish motive. As Harris pulled into his office on June 18, 2014, the day Cooper died, he told a woman who had shared her own problems with him, "Agreed, hug, we both need that," according to the detective.

Stoddard shared snippets of his interviews with three of the minors. According to the detective, Harris spoke to six women or girls on the day Cooper died.

One minor, identified only as "CD," told Stoddard that "Ross loved Cooper a lot" and he would never do anything to hurt the child, the detective said, adding that "CD" also told him that though he admitted cheating on his wife, Leanna, he loved her and would never leave her. She further said that Harris sent her images of him and Cooper -- whom he called "smart" and "handsome" -- vacationing at a beach, while she shared photos from her prom, Stoddard said.

At one point in their relationship, Harris discouraged her from dropping out of a technical school, the detective said. Asked why she sent him photos, she replied, "Because I really liked him," she said, according to Stoddard.

The two conversed while Cooper was dying in the car, Stoddard said, adding that the communications were sexual in nature.

Asked if he thought Harris' motive was financial or if he missed his pre-fatherhood freedom, the detective replied, "I think it's all of it."

Pressed on reports that Harris and his wife conducted online searches related to "child-free" lifestyles and participated in a "child-free" forum on Reddit, Stoddard said Harris did not actively search for the term "child-free." He merely clicked on three Reddit posts, the detective said, adding that he had no evidence that Harris and his wife conspired to kill Cooper.

"None of that suggests that (Harris) adheres to motive to murder his child, but it sounded good at the probable cause hearing didn't it?" Kilgore said to Stoddard.

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Recalling another interview with a minor identified as "JM," Stoddard said Harris told the teen he loved her and missed her and once surprised her by showing up in the parking lot of a store she had said she was going to. The day before Cooper died, Harris said to "JM" on the messaging service Kik, "You're gone again?" referring to her absence on the app and on the morning of Cooper's death he sent her a Kik message wishing her a good morning, Stoddard said.

At some point, Harris told "JM" that his wife had discovered their chats.

Stoddard detailed a conversation with a third minor, identified as "CH," who asked him, "Do you love your wife?" Harris replied in the affirmative but said the relationship was in a bad state. He also told "CH" he was a sex addict, the detective said.

Leanna Harris was not in court for Monday's hearing.

Harris faces charges of malice murder, two counts of felony murder, first-degree cruelty to children, second-degree cruelty to children, criminal attempt to commit a felony (sexual exploitation of a minor) and two counts of dissemination of harmful material to minors.

According to the indictment against Harris, the sexual exploitation and dissemination of harmful material charges involve Harris requesting a nude photo of a minor's genitalia and sending her descriptions of "sexual excitement and sexual conduct." Stoddard says Harris also sent one girl a photo of his erect penis.

Stoddard and Kilgore concurred that Harris requested images of "CD's" genitalia on three occasions, once in March 2014, once in May 2014 and on the day Cooper died. Stoddard also outlined a graphic communication in which Harris gave "CD" advice about her juvenile boyfriend, a line of testimony to which the defense objected, accusing prosecutors of showing off for the media on hand.

Grilled during cross-examination on whether police had charged Harris with child pornography, Stoddard said no but added that investigators found evidence of child porn on his phone via Whisper, where he used the pseudonym, "Morgan Freeman's penis."

Elaborating, the detective said that in one instance "a young lady" sent Harris a photo of her genitalia and said, "Can I be honest?"

"Yeah," Harris allegedly replied.

"I am 15," she said, according to the detective, prompting Harris to respond, "Oh, that's a nice (expletive) for 15." Later, in response to her message about older men, Harris replied, "Show me more. Haha. Make me a naughty older man," Stoddard testified.

She then sent a photo of her genitalia in the mirror, and he responded by asking her to bend over and saying, "Make me a huge perv."

Under questioning from Kilgore, Stoddard said he didn't know the girl's age.

Harris' defense team had hoped to have the charges related to sexting minors severed from the charges related to Cooper's death, which Staley denied. The prosecution argued that while establishing motive was not a requirement in this case, the nature of the texts backs the prosecution theory that he no longer wanted the burden of a family.

Prosecutors in January said they would not seek the death penalty against Harris

Staley proposed a February trial date for Harris, but the defense said it would need until the end of January to argue all its motions. Staley set a hearing for December 14 and gave Harris' lawyers until January 22.