Bianca Devins, 17, traveled hours from her home in upstate New York on Saturday night to go to a concert in New York City with a young man she’d been seeing, the police said.
In the morning, Ms. Devins was found dead, lying on the ground next to an S.U.V., back in her hometown, Utica.
Her throat had been slit by the young man, Brandon Clark, who then posted grisly photos of her body on social media before stabbing himself in front of officers who, after a brief struggle, arrested him, the police said.
On Monday, as the news of Ms. Devins’s killing spread online with the hashtag #ripbianca, the disturbing photos proliferated on Instagram, where they were shared and reshared even as the posts were being reported by users and removed by the platforms.
The shocking images prompted a widespread outcry about the spread of violent content on social media and the inability by tech companies to police it. At the same time, there was rampant speculation as people scoured Ms. Devins’s online history, trying to determine whether her death was a case of internet harassment that had spilled into real-life violence.
On Monday night, Mr. Clark, 21, of Cicero, N.Y., was charged with second-degree murder. He was in the custody of the sheriff’s department at a hospital in Utica, where he had been in critical condition but expected to survive, according to a police spokesman, Lt. Bryan Coromato.
In a statement, Ms. Devins’s family described her as “a talented artist” who, after graduating high school last month, was preparing for college in the fall.
“Bianca’s smile brightened our lives,” the statement said. “She will always be remembered as our Princess.”
Mr. Clark’s family could not immediately be reached for comment.
Officers arrived at the scene some time after 7 a.m. on Sunday after multiple phone calls, including one from Mr. Clark, the police said. In the call, he had “made incriminating statements” and alluded to wanting to harm himself.
When officers arrived, officials said, they found Mr. Clark lying down next to a black S.U.V.
As soon as they approached, he began stabbing himself in the neck. Shortly after, the police said, he laid his body across a green tarp that was covering something on the ground and began taking photos of himself. The officers later learned the tarp was covering Ms. Devins’s nearly decapitated body.
Screenshots show that Mr. Clark posted photos of himself to Snapchat in which he was bleeding from a neck injury and lying on a tarp like the one that the police had described.
After more officers arrived at the scene, they were able to get close enough to Mr. Clark to disarm and arrest him.
Gruesome pictures posted to Mr. Clark’s Instagram account on Sunday showed Ms. Devins’s corpse and the caption, “I’m sorry Bianca.” In the time leading up to the killing, Mr. Clark had also posted a photo from inside a car with the caption, “Here comes Hell. It’s redemption, right?”
After her death, Mr. Clark posted photos of Ms. Devins’s bloodied body on a server on the chat platform Discord that she was known to frequent, the police said. Screenshots show a person posting photos of the killing and claiming to have committed it, then taunting Ms. Devins’s followers.
Lieutenant Coromato said that the police were looking at the posts, as well as similar ones on the anonymous message board 4chan, as part of their investigation.
The police confirmed the authenticity of the photographs and said it had contacted Discord for more information.
“We are working closely with law enforcement to provide any assistance we can,” said a Discord spokesman in a statement. “In the meantime, our hearts go out to Bianca’s family and loved ones.”
As of Monday morning, the Discord server where the picture and messages were posted was no longer publicly accessible. Mr. Clark’s posts had expired from his Instagram and Snapchat stories, where content disappears after 24 hours.
Instagram had removed Mr. Clark’s account by Monday afternoon, but before it was deleted, his profile read “10/06/1997 — 7/14/19. Just know that I feel no pain now.”
A spokeswoman for Instagram said in a statement: “Our thoughts go out to those affected by this tragic event. We are taking every measure to remove this content from our platforms.”
Investigators believe that Ms. Devins and Mr. Clark first connected on Instagram two months ago, the police said. They traded messages for a while before their relationship became a “personally intimate” one, and the two had met each other’s families, the police said.
On Saturday night, Ms. Devins and Mr. Clark planned to attend a concert together in New York City, about 250 miles from Utica, and at some point during the night, the two had an argument at the concert venue, the police said. They did not identify the venue or provide specifics.
The relatively scant information released initially by the police on Sunday fueled rampant speculation about the killing. On social media, many people portrayed Mr. Clark as an obsessed stalker of Ms. Devins, who had thousands of Instagram followers. Rumors spread that he had tracked her to the concert in New York City before eventually killing her.
So far, the police do not have evidence suggesting that to be the case, Lieutenant Coromato said.
Susan Beachy contributed research.