A law enforcement source speaking to the Investigative Project on Terrorism claims evidence indicates the gunmen who attempted to attack a Draw Muhammad Contest in Garland, Texas on Sunday were reacting to social media posts specifically demanding a terror attack against the event.

According to the IPT source, social media postings about the event began appearing en masse about three days earlier. They featured vicious exhortations to kill those responsible, urged beheadings and mass killings. Simpson, who court records show had a long affinity with jihadist causes, apparently saw some of those calls to violence and headed to Texas intending to kill as many of the Garland conference attendees as possible.

It is not yet known what prompted the late-hour focus on the Garland meeting within foreign jihadi circles, but investigators are confident Simpson and Soofi were trying to respond to those specific calls for jihad.

At this point, authorities do not believe the attack was well planned or that Simpson and Soofi ever conducted reconnaissance on the Culwell Center before coming out guns blazing.

If they had, they might have discovered that organizers, well aware of the inherent threat of violence an event like theirs carries, paid $10,000 to hire off-duty police to provide security. That was in addition to the security provided by members of Garland’s SWAT team, along with FBI and ATF agents.

On Friday, the FBI issued an intelligence bulletin in Texas downplaying the possibility of any violence that could erupt, the IPT learned. The FBI said in the classified bulletin that no evidence had surfaced in the United States from any sources that there was any credible threat of violence at the Muhammad Art Exhibit and Contest.

However, another intelligence unit in Texas disagreed with the FBI assessment and issued a different intelligence warning citing a “massive amount of overseas incitement to carry out violence on social media.” The calls for violence—including exhortations to “destroy Texas” from Islamist-sympathizers in Europe.

Read the full report at the Investigative Project on Terrorism.