BOSTON (CBS) – A Plainville teenager faces charges of involuntary manslaughter after investigators say she encouraged a fellow high school student to commit suicide in 2014.

Police say 18-year-old Conrad Roy committed suicide on July 13, 2014, behind a K-Mart in Fairhaven. Roy was a resident of Fairhaven and Mattapoisett.

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The Bristol District Attorney’s office confirmed to WBZ-TV that Michelle Carter, 18, was indicted on February 5 after a lengthy investigation showed that she “strongly influenced” Roy’s decision to kill himself.

According to the district attorney’s office, after finding Roy dead inside his truck, police searched Roy’s cell phone and found he had been text messaging Carter up until his death, which was caused by carbon monoxide poisoning.

“It is alleged that Ms. Carter had firsthand knowledge of Roy’s suicidal thoughts,” the district attorney’s office said. “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.”

Conrad Roy. (Image Credit: Facebook)

Conrad Roy. (Image Credit: Facebook)

Carter was arraigned in New Bedford Juvenile Court on February 6 and released on $2,500 bail.

District Attorney Thomas Quinn recused himself from the case because he has a relationship with Roy’s family.

Michelle Carter (WBZ-TV)

Michelle Carter (WBZ-TV)

Court documents show more than 1,000 text messages between Carter and Roy in the days leading up to his death. At one point shortly before he died, Roy became scared and said he did not want to leave his family. As a result he stepped out of his truck, investigators said.

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Court documents show that Carter told Roy to “get back in.”

“He was having problems with depression for a few years,” Conrad’s grandmother Janice Roy said. “But we were hoping, he seemed to be pulling out of it.”

Asked if he could be easily manipulated by someone else, Roy’s grandmother said, “he was in a fragile state. But I think he could have been manipulated not to.”

After learning of the texts between her grandson and Carter, she said, “I felt like the blood drained out of me. I don’t believe this, it’s too horrific.”

Joseph Cataldo, Michelle Carter’s attorney, believes the district attorney is overreaching in charging her with involuntary manslaughter. “She was not even present when he made a decision, a voluntary, conscious decision to end his own life,” Cataldo said.

King Philip Regional School District, where Carter is a student, declined comment on the case.

“The circumstances surrounding this tragic loss are under investigation. Our deepest sympathy is extended to the family and school community of Conrad Roy,” said Superintendent Elizabeth Zielinski. “As an educational institution we are bound by regulations related to the privacy of student records. As such I will not comment on the situation, or discuss anything that is related to any students record.”

Carter is next scheduled to appear in New Bedford Juvenile Court for a pretrial hearing on April 17.

For information about suicide prevention visit the National Suicide Prevention Lifeline or call 1 (800) 273-8255.

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WBZ-TV’s Beth Germano contributed to this report.