The FBI sent a bulletin to the Garland Police Department about suspected shooter Elton Simpson three hours before the start of Sunday's Draw Muhammad art contest at the Curtis Culwell Center, NBC News' Pete Williams has learned.
The FBI, according to NBC News, said Simpson was "interested in the event" but that FBI Director James Comey said they had no reason to believe he intended to attack the event and didn't know he was on his way to Garland.
Comey also said he did not believe the officer who shot Simpson and Soofi Nadir, originally known and published as Nadir Soofi, was aware of the FBI bulletin.
Comey said the FBI investigation into Simpson and Nadir is ongoing.
According to Comey, the Texas plot is a dramatic example of the changing nature of terror threats and the FBI now has hundreds of investigations of potential home grown extremists under way, with cases open in every state.
"I know there are other Elton Simpsons out there," Comey said. "Only a few years ago ... if someone wanted jihadist propaganda, they would have to go find it on the Internet. So we focused on the places they'd go."
Messages from terrorist groups such as ISIS are now pushed into the pockets of people who are interested in it through social media.
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"Its recruiting and tasking at the same time. The old distinction between inspiration and direction is no longer relevant," Comey said, adding that hundreds of people in the US - maybe thousands - "are consuming this poison."
While Comey said investigators can follow messages that are posted on public twitter accounts, ISIS recruiters are steering people off Twitter into encrypted forums, which the government cannot see.
Comey said finding other Elton Simpsons in the US is a "very hard task."
"We have hundreds working on it around the clock. But in almost every case of violence," he said, "Someone saw something. A friend, a family member. Its more important than ever for people to speak up."