Michelle Carter, 18, has been charged with manslaughter in the death of Conrad Roy III

An 18-year-old girl has been charged with manslaughter for urging her friend to commit suicide.

Conrad Roy III, 18, committed suicide last summer in a Kmart parking lot in Fairhaven, Massachusetts. But now investigators say his friend Michelle Carter, also 18, may have encouraged him to do it, WBZ-TV reports.

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“It is alleged that Ms. Carter had firsthand knowledge of Roy’s suicidal thoughts,” the Bristol District Attorney’s office said in a statement Thursday to the Sun Chronicle.

“Instead of attempting to assist him or notify his family or school officials, Ms. Carter is alleged to have strongly influenced his decision to take his own life, encouraged him to commit suicide and guided him in his engagement of activities which led to his death.”

Roy was found dead of carbon monoxide poisoning in his truck on July 13, 2014. Police first became suspicious after reading a series of text messages between Carter and Roy in the days leading to his death. Altogether, they exchanged more than a thousand texts, the Fairhaven Neighborhood News reports.

In a police report provided to the Chronicle, Fairhaven police Detective Scott Gordon writes: “Not only did Conrad tell Carter in several of his texts prior to his death that he was scared and didn’t want to leave his family, she continued to encourage him to take his own life, and when he actually started to carry out the act, he got scared again and exited his truck, but instead of telling him to stay out of the truck Carter told him to ‘get back in.’ ”

Carter’s attorney, Joseph P. Cataldo, told the Standard-Times of New Bedford on Thursday night that the 18-year-old girl is innocent.

“This is terrible tragedy – a young man taking his own life,” he said. The district attorney’s office “is trying to pin the blame on someone. I can’t understand why they brought the charge.”

He added: “They’re trying to claim there is manslaughter when they freely admit the boy took his own life. You can’t have it both ways.”

Carter Tweeted about missing Roy after his death, writing on Sept. 12, 2014, “Happy birthday to my Conrad. Forever in my heart. I hope the angels sing to you today.”

She also took part in a fundraiser for Roy, Tweeting on Sept. 13, 2014, that it had raised $2,300.

Carter’s most recent Tweet about her friend came earlier this month following a parade in his honor.