Law-enforcement agencies and intelligence and security services around the world have been taking note. In 2014 the International Association of Chiefs of Police conducted its fifth annual survey on law enforcement's use of social media. Surveying 600 agencies in 46 states, the research found that the most common use of social media is for criminal investigations (82.3 percent). Meanwhile, it found the most frequently used social media platforms are Facebook (95.4 percent), Twitter (66.4 percent) and YouTube (38.5 percent).
In 2011 the New York Police Department formed a unit to track criminals who brag about their crimes on Twitter, MySpace and Facebook. And in March 2013, following the fatal attack of a soldier in London, an intelligence unit within London's Metropolitan Police Service focused on tracking social media feedback and monitoring community tension.
"I think that social media gives huge insight into the mental instability of desperate people," Miller said. "As a society, we should use our advances in machine learning and big data analytics to identify these people that are in need of help before tragedies, like the latest Oregon shooting, occur."
Michael Levine, a law-enforcement consultant and retired Drug Enforcement Administration agent, said social media should be used as an investigative tool and, in the best-case scenario, to obtain probable cause for a search warrant. But he also sees major limitations on its usefulness in the legal system.
"Both the Oregon shooter and his mother had a history of social media posts, which shed light on the buildup toward the tragedy. However, before the shooting, there was no court-worthy evidence that the mere participation in social media played a causative role in any mass shooting," Levine said.
Levine added that after a crime, it's different. "Once a shooting has occurred, an investigator can find court-worthy evidence of other people playing a criminal role and aiding and abetting and/or encouraging the act; sufficient evidence to indict." But he added that as a career criminal investigator, trial consultant and expert witness, he saw no logical or causative relationship that would be acceptable as "evidence" by a court in the specific case of the Oregon shooting.