When Dylann Roof gunned down nine black parishioners at a South Carolina church in June, investigators later discovered a racist manifesto posted online.
After Mark Lavoie shot and killed his wife in a New Hampshire hospital bed in January, and then turned the gun on himself, police found a Facebook post in which Lavoie warned of his actions.
That’s usually how it goes — authorities are left to comb the Internet for clues about a suspect’s motives once a tragic event has already unfolded.
Wednesday’s fatal shooting of two television journalists in Virginia stands out for the real-time manner in which the alleged gunman, Vester Lee Flanagan II, chronicled his attack and explained his reasons on social media as he fled.
In instant, digital relief, Flanagan demonstrated a dark capability of the mobile devices many of us carry constantly.
The odds are that he won’t be the last to do so. In an age when people mount GoPros on their ski helmets, take selfies on roller coasters, and live tweet their weddings, why wouldn’t criminals document themselves in the act?
“Social media is going to carry over into every aspect of our lives,” said Janet Johnson, a social media specialist at the University of Texas Dallas. “We cannot prevent criminals from using it.”
Flanagan, a 41-year-old former news anchor who had worked with the victims at WDBJ-TV in Roanoke, seemed more interested in attracting an audience than getting away with murder.
“I filmed the shooting see Facebook,” he tweeted under the name Bryce Williams, which he used on the air.
Indeed, Flanagan recorded a first-person video Wednesday as he approached reporter Alison Parker, 24, and cameraman Adam Ward, 27, and opened fire. He quickly posted the footage, which shows him stalking Parker and Ward as they conduct a live interview, pointing a black handgun in their direction, and firing several shots.
Flanagan left the scene of the shooting, tweeting while on the run: “Alison made racist comments,” he wrote in one post. In another, he stated that Adam had reported him to the station’s human resources department “after working with me one time!!!”
Flanagan shot himself later Wednesday morning, as police pursued him on Interstate 66. He was taken to a nearby hospital, where he died in the afternoon.
Twitter and Facebook suspended Flanagan’s accounts, but not before the video and messages were widely viewed and republished elsewhere on the Internet.
It is unclear why the social networks allowed Flanagan’s accounts to remain active for several hours after the shooting, or why they ultimately shut them down. A Twitter spokesman said “we don’t comment on individual accounts,” and declined to answer general questions about account management in manhunt situations.
Spokesmen for Facebook and the Virginia State Police did not respond to Globe inquiries.
Twitter and Facebook appear to have had no legal obligation to disable Flanagan’s accounts, and it is possible that they allowed him to continue posting in an effort to aid law enforcement, said Deven Desai, an associate professor of law and ethics at the Georgia Institute of Technology.
“It might be poor taste,” he said. “Letting someone celebrate their mania doesn’t seem like a good thing. But for all we know, they were asked to leave him active as police tracked him.”
There’s another reason why social networks might have been slow to disable Flanagan’s accounts, according to Stephen Handelman, director of the Center on Media, Crime and Justice at the John Jay College of Criminal Justice in New York City.
“Particularly when we’re talking about alleged gunmen or suspects, dropping their accounts — unless they are actively encouraging others to commit crimes — seems a free-speech issue,” he said.
Danielle Keats Citron, a law professor at the University of Maryland, noted that social networks often work with police in long-term investigations involving child pornography and exploitation. But in a fast-moving case, such as Wednesday’s shooting and subsequent chase, the responsibilities of social networks are unsettled.
“In an ongoing crisis situation, I imagine that social media providers would assist law enforcement to help deescalate or mitigate harm,” Citron said.
“Of course, that does not mean social media would help without proper legal process, like a warrant.”
RELATED:email@example.com. Follow him on Twitter @callumborchers.