BOSTON (AP) — Massachusetts' highest court has ruled that a teenage girl must stand trial on a manslaughter charge for encouraging her boyfriend to kill himself by sending him dozens of text messages and telling him to "get back in" a truck filled with carbon monoxide fumes.

The Supreme Judicial Court ruled Friday that a grand jury had probable cause to indict Michelle Carter in the 2014 death of 18-year-old Carter Roy III.

Carter's lawyer said her texts were protected by the First Amendment and didn't cause Roy to kill himself.

But the court noted that the grand jury heard evidence suggesting that Carter engaged in a "systematic campaign of coercion" that targeted Roy's insecurities and that her instruction to "get back in" his truck in his final moments was a "direct, causal link to his death."

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