"Lone wolf actors are the things that will keep law enforcement officers awake at night," said Thomas Brady.
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Brady runs the College of DuPage's Homeland Security Training Institute.
Their "main street" training site is a fully built-out street scene where students and first responders can practice for real life threats, such as mass shootings carried out by radicalized individuals.
"There might be an actor who's planning something, but he's never been pulled over by the police, has never had contact with the police, has never been arrested," Brady said. "It becomes very a very scary thing when somebody does one of these acts and no one's ever heard of them before."
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A lone gunman, who wasn't on the radar of police before the attack, killed nearly 60 people in the 2017 Las Vegas massacre. His motives have never been revealed.
Just this year, from the supermarket shooting in Buffalo to the Uvalde elementary school attack, to right here in Highland Park on the 4th of July, lone actors are continuing to plan and carry out devastating attacks.
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"The FBI and Homeland Security have warned the most significant terrorism related threat facing the United States today comes from lone offenders, individuals who self-connect with extremists ideological belief system, or cultivated personal grievance, who based on those ideological beliefs or grievances, go out and commit mass casualty attacks," said ABC News Contributor John Cohen.
Cohen is the former counterterrorism coordinator at the Department of Homeland Security and is an expert on mass shootings. He told the I-Team there are a number of steps law enforcement and local communities can take to address these threats of mass violence.
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"Law enforcement organizations need to work closely with members of the communities so that behaviors are observed that represent warning signs that someone may be traveling down the path toward violence," Cohen said.
"Law enforcement and civilians need to kind of work together to solve this problem," Brady added. "Say something if someone's struggling. Help them reach out to them, get them the help that they need. That can alleviate a lot of these instances because it can prevent a mass casualty attack from happening."
Lone wolf threats don't always exist in a vacuum. They frequently fester on social media. Law enforcement officials tell the I-Team red flag laws need to be applied to limit firearm access for potentially dangerous individuals and lone wolf experts say public concerns need to be reported and thoroughly investigated, in hopes of preventing the next attack.