Did Michelle Carter Really Tell Boyfriend to 'Get Back In' Truck to Kill Himself?

Three words — “get back in” — put Michelle Carter in jail for the involuntary manslaughter of her teenage boyfriend, who killed himself by inhaling a fog of poisonous carbon monoxide inside the cab of his pickup as it sat in a Kmart parking lot in July 2014.

With those three words, relayed by Carter over the phone to 18-year-old Conrad Roy III as he panicked and got out of the truck, Carter crossed the line from concerned but supportive ally to killer, effectively pushing him to carry out his suicide, a judge ruled.

But did she actually say them?

It’s a question raised in the new two-part HBO documentary film I Love You, Now Die: The Commonwealth v. Michelle Carter, premiering Tuesday, July 9 and Wednesday, 10 (8 p.m. ET/7 p.m. CT), and by Dr. Peter Breggin, a clinical psychiatrist who worked for Carter’s defense attorneys, who says of Carter, “She is a colossal liar.”

On Monday, Carter’s legal team appealed her conviction and 15-month sentence to the U.S. Supreme Court, according to The Washington Post. The appeal revisits their prior argument that Carter’s statements to Roy in thousands of texts and emails over two years — a handful of which propose suicide options along with Carter’s encouragement for Roy kill himself, as he vowed to do — amount to free speech and not a criminal act.

RELATED: Mass. Woman Sent to Jail for Sending Texts to Teen Boyfriend Urging Him to Kill Himself

A Massachusetts state appeals court had earlier rejected that argument in upholding Carter’s conviction and sentence.

The two Massachusetts teens lived an hour apart, and had crossed paths while on vacation with their respective families in Florida. Although Carter was nowhere near Roy at the time he died, her texts to his family and others in the hours before and after reveal her intent to mislead them about his actions and whereabouts, as she was in contact with him throughout.

RELATED: Warning Signs to Look for If You Are Concerned Someone Is Suicidal

Documentary director Erin Lee Carr‘s film offers deep profiles of the troubled teens, both of whom were on prescribed medication for depression and had attempted suicide earlier, as they are drawn together in a relationship lived almost entirely through social media toward its tragic end.

As for Carter’s statement in a text two months afterward to a friend that she’d been on the phone with Roy and told him to “get back in” his truck when he became scared that he might actually die, no other documentation backs it up, says Breggin.

RELATED: Mass. Teen Who Urged Boyfriend to Kill Himself in Texts Says It Was Free Speech, Not Crime

Speaking to PEOPLE, he surmises that a distraught Carter may have fictively accepted the blame as a way to deal with her own grief.

“This was said in a state of morbid upset,” he says. “They promised to talk to each other after his death. He wrote in his suicide note that she was the only one who understood what he was going through.”

By the time Carter, now 22, typed that statement to her friend, Samantha Boardman, “she had dozens and dozens of times texted him in heaven,” says Breggin. “There’s no reason to believe that her statement wasn’t another aspect of her disturbed mind.”

Carter had just been in contact with Roy’s divorced mom, who agonized over her failure after Roy’s death to protect him from what his mom perceived as the bad influence of Roy’s father, who previously had been arrested by police for assaulting his son, says Breggin.

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“After (Carter) texted his mother and his mother says ‘I’m to blame,’ she writes back to his mother, ‘no, you’re not to blame.’ And then she writes Boardman, ‘I’m to blame,'” he says.

Prosecutors emphasized the “get back in” text in their trial narrative that Carter, then 17, was a lonely young woman scorned by others she tried to befriend, and who manipulated Roy toward his death in an effort to make herself a center of attention and sympathy.

But Breggin argues that Carter herself was being manipulated by Roy, who had multiple hospitalizations and prior suicide attempts, and at one point told Carter that he’d seen the devil. “He said to her, ‘the devil has put us together.’ He is actually the leader,” says Breggin.

“He tells her he’s going to kill himself and there’s nothing she can do about it. She actually does try to do something about it,” urging him toward help after those initial written texts to her, he says.

“She is fighting him killing himself, because she thinks that’s her job in life, is to help people,” he says.

Roy’s response: “He tells her that is she ever tries to stop him again, he won’t talk to her,” he says.

Those statements carried little weight at Carter’s trial, says Breggin, who notes that prosecutors insisted on the absolute truth of Carter’s “get back in” text while dismissing others that led Carter’s acquaintances to disbelieve what she often told them — as when she flipped on whether she’d had sex, or possibly even been raped, by Roy.

In the film he says of the “get back in” text cited by the judge and prosecution: “I don’t think that we can know that Michelle’s story is true at all.”

The two-part HBO documentary film I Love You, Now Die: The Commonwealth v. Michelle Carter debuts July 9 and 10 (8 p.m. ET/7 p.m. CT).

If you or someone you know is considering suicide, please contact the National Suicide Prevention Lifeline at 1-800-273-TALK (8255), text “home” to the Crisis Text Line at 741-741 or go to suicidepreventionlifeline.org.