(WASHINGTON) -- A convicted stalker from Colorado is asking the Supreme Court this week to toss out the law that put him in prison for sending hundreds of messages on social media to a singer-songwriter who felt threatened by the contact.
Billy Raymond Counterman, who spent four-and-a-half years behind bars, says he never intended to harm rising-star performer Coles Whalen, whom he'd never met, and that the First Amendment protects his ability to communicate with a public figure.
Whalen said she feared for her life and that the years of incessant messages from Counterman on Facebook inflicted significant emotional distress and sent her into hiding. She no longer performs openly in public.
"It's very unfortunate that another individual, completely unprovoked, would be able to take that opportunity from her, to live the life that she wanted to live," Marita Whalen, Coles' younger sister and former roommate, said in an interview with ABC News.
The First Amendment protects most speech but not libel, obscenity or what the Supreme Court has called "true threats." Those can result in prosecution.
In taking up Counterman's appeal, the justices are set to clarify when a threat becomes a crime.
"The question here is whether you have to prove intent before you can put someone in prison for making a 'true threat,'" said Jay Schweikert, a research fellow at the Cato Institute, one of several groups, including the American Civil Liberties Union, that say punishing Counterman was wrong.
"No one's here defending the messages that he was sending as model behavior for how to communicate with a public figure," Schweikert told ABC News. "It's whether it constituted a threat for which he could be put in prison for four and a half years."
"We have a lot of heated speech online," he added, "and the First Amendment does not allow the government to make that a crime."
Counterman first made contact with Whalen in 2010, but the tone and frequency of his messages evolved over the six years that followed.
Though Whalen never responded, Counterman's communications ranged from the familiar -- "I'm going to the store would you like anything?" -- to the unsettling: "I'm currently unsupervised. I know, it freaks me out too, but the possibilities are endless."
Some messages, Marita Whalen said, were downright alarming.
"You're not being good for human relations. Die. Don't need you," Counterman wrote Coles Whalen in one missive.
"There were messages where Mr. Counterman would reference details about where [Coles] had been or the vehicle she was driving, who she was hanging out with," Marita Whalen said. "It had a significant impact on her -- that lightheartedness that she used to always carry, sharing that joy with other people, it really got dampened. She became much more protective and afraid."
Coles Whalen was so afraid, her sister said, that she got a permit to carry a gun, hired a bodyguard for some concerts and went to court to obtain a restraining order against Counterman even though she had never seen him in person.
Coles Whalen declined ABC News' request for an interview to protect her privacy and security.
"We were convinced that he was an unstable individual and his actions would be unpredictable. We felt that he was very dangerous, and law enforcement agreed," Marita Whalen said.
Colorado law says threats become illegal when a "reasonable person" would suffer "serious emotional distress" from the communications.
In 2016, authorities arrested and charged Counterman with "stalking -- serious emotional distress." A jury later convicted him, and a judge imposed a sentence of four-and-a-half years behind bars.
"Under Colorado law, the specific intent of the stalker, in this case, is not the relevant factor," Colorado Attorney General Phil Weiser told ABC News. "It's whether the victim would reasonably experience the fear of physical violence because of the nature of the threats."
Counterman, who has already completed his sentence, argues in court documents that not having to prove intent risks "essentially criminalizing misunderstandings."
"If the Supreme Court upholds this conviction, then a huge swath of online speech is open to potential criminal prosecution," Schweikert said.
But experts say a balancing act is required in the digital age and that law enforcement is in a tough spot.
"In a case of stalking, stalkers are often oblivious to reality. And if you require the state to have to show that they understood that their words were threatening and creating this fear of physical violence, you could actually let a lot of stalkers go," Weiser said.
"This case is about establishing a precedent that will govern not just the law of stalking, but cases of domestic violence, threats against schools or houses of worship and many other contexts," the attorney general added.
As the high court now takes up the debate, the Whalen family said they hope the justices don't reopen old wounds with a decision overturning Counterman's conviction.
"It's terrifying, honestly, to think that we might go back to a place where a victim might feel that they're not going to believe me that this is truly threatening when clearly she felt that her life was at stake," Marita Whalen said.
As for Coles Whalen: "She is incredibly resilient and a very strong person," Marita Whalen added. "She has that inherent spark of joy within her, and really there's no life circumstance or individual that can take that from her."
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