However depressingly common gun violence has become in the United States, high-profile cases continue to shock us. And yesterday, the news that a Virginia television crew had been murdered during a live broadcast only became more horrifying after the suspect, Vester Lee Flanagan II, posted what appeared to be his own video of the killings before committing suicide.

But however sickening Flanagan's broadcast was, he was hardly the first person to take advantage of technological advancements to self-publish material related to a murder. And self-publishing is a natural, if unpleasant, evolution in the long relationship between killers and the media. Flanagan's postings were probably inevitable, as may be a new kind of horror: a killing that's not just broadcast, but live-streamed.

The relationship between murderers and media outlets flows both ways; reporters have long recognized the news value in reaching out to a killer, sometimes even when a crime is in progress. When Howard Unruh embarked on the 1949 massacre of his neighbors that would become known as the "Walk of Death," Camden Evening Courier writer Philip W. Buxton reached Unruh on the phone after he barricaded himself in his mother's apartment - the number was in the phone book. Buxton got out two questions before police started moving in on the apartment.

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Thirty years later, two reporters from the San Diego Evening Tribune who were calling spree killer Brenda Spencer's neighbors to report out her mass shooting ended up reaching Spencer herself. Her explanation for the murders - "I don't like Mondays" - became part of pop culture history.

And killers sometimes reach out to the media, either before or during their acts. During his 2006 mass shooting at the Jewish Federation of Greater Seattle, Naveed Afzal Haq both talked about wanting to speak with reporters from CNN and asked an emergency dispatcher to patch him through to the network, a request she said she couldn't grant. Adam Lanza, who killed 20 students and six adults at Sandy Hook Elementary School in 2012, is believed to have previously called in to a college radio station in Oregon to discuss a chimpanzee that had attacked a human, making a comparison between the animal and mass shooters.

While Haq's attempt at outreach seemed somewhat spontaneous, and Lanza's call was not directly linked to his crime, some murderers send material to the media that's intended to arrive as they carry out their killings, amplifying the terror and explaining their actions. Mark Essex, who killed nine people and wounded 13 in two separate series of attacks on Dec. 31, 1972, and Jan. 7, 1973, sent a letter to WWL-TV, a New Orleans television station, before the Dec. 31 killings giving notice that he planned to attack the city's police department on New Year's Eve.

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Seung-Hui Cho, who killed 32 people at Virginia Tech in 2007, mailed a statement, photos and a series of videos to NBC News; the package arrived after Cho began his attack. Two years later, Jiverly Antares Wong mailed a similar package to a Syracuse, New York, television station the day he carried out a shooting at the Binghamton American Civic Association; he had taken English classes at the association, and shot the organization's receptionists before opening fire in an English-as-a-second-language class.

And Flanagan's distribution of video of actual killings has a precedent in Mohammed Merah's shootings in two cities in France. Merah wore a GoPro camera during the attacks, and someone who claimed to be one of Merah's accomplices sent an edited version of the footage to Al Jazeera, which declined to air it.

As Merah's example illustrates, killers who reach out to reporters or send material to media outlets are relying on other people and organizations to broadcast their words. Television stations and newspapers may decide not to publish the material murderers send them because they do not want to compromise law enforcement investigations, because they do not want to give killers platforms, or out of respect for survivors and the families of the dead. So it's no surprise that as social media has made all sorts of self-publishing easier than ever that killers have begun to distribute their own manifestos and videos of their actions themselves.

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In "One of Us," Asne Seierstad's book about Anders Behring Breivik's 2011 bombing of government buildings in Oslo and shootings of 69 people at the summer youth camp for the Norwegian Labor Party, she notes that a critical part of Breivik's plan was the distribution of a racist, largely plagiarized manifesto that railed against Muslim immigrants.

"Once the manifesto had been sent to a thousand email addresses, everything ground to a halt," Seierstad reports. "Telenor's spam filter had detected that the upper limit for the number of messages that could be sent per day had been reached." Social media has no spam filter and no editors to express qualms about publication. Jared Lee Loughner, who shot a number of people including then-U.S. Rep. Gabrielle Giffords in Tucson, Arizona, in 2011, posted about his political beliefs and the definition of terrorism on MySpace and YouTube in the days leading up to his attack.

Elliot Rodger, who killed six people in Isla Vista, California, in 2014 in an attack apparently motivated by his lack of sexual success, both emailed a manifesto to a number of acquaintances and posted a YouTube video announcing his intentions. And Dylann Roof, who is the suspect in the June 17 killing of nine people at Emanuel African Methodist Episcopal Church in Charleston, South Carolina, apparently registered a website with the title "The Last Rhodesian" in February and posted a manifesto that explained his motivations.

Flanagan himself worked in media: The reporter and cameraman he killed were his colleagues. His crime exploited the live nature of the broadcast to make sure people would see his crime. Posting the video himself extended the reach of his terror beyond the local market for the broadcast, and beyond anyone who was watching in the original time slot. Flanagan may have known more than other members of his deadly fraternity about how to make himself seen, but he's hardly alone in the desire to have his awful acts witnessed and acknowledged.

Flanagan won't be the last, either. As sickening as Monday's broadcasts were - my startled deskmates and I jumped when one of our colleagues played Flanagan's video in the newsroom - I'm afraid that worse is yet to come. Can it be long before a killer live-streams his terrible work? Technology, and an accelerating rate of mass killings, seems to make such an outcome inevitable.

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Rosenberg writes The Post's Act Four blog.