Of course they did, but it’s far from clear just how much involvement ISIS had in the attempt to massacre attendees at the free-speech event in Garland, Texas. Elton Simpson had already appeared on counter-terrorism radar, having been convicted in 2011 when he attempted to travel to Somalia to join other Islamists in terror operations, and then lied about his plans to the FBI. Did ISIS command Simpson to attack the event, or are they just glomming onto the failure of Simpson and his roommate, Nadir Soofi:

“Two soldiers … of the caliphate attacked an exhibit in Garland in American Texas, and this exhibit was holding a contest for drawings offensive to the Prophet Muhammad,” the militant group said on its al-Bayan radio station, according to the SITE Intelligence Group, which monitors radical factions around the world.

The statement warned that the United States will be targeted by other Islamic State fighters waging attacks that will be “worse and more bitter, and you will see from the soldiers of the Islam State what will hurt you,” the SITE report said.

The claim, however, offered no hints about how the Islamic State purportedly made contact or directed the two attackers from Phoenix in Sunday’s failed assault.

CBS News also picks up on the claim, and follows up with a heartbreaking interview with Soofi’s mother, who still can’t understand what happened to her son:

The other gunman, Nadir Soofi, was not on law enforcement agencies’ radar screens prior to the attack, says Pegues.

Soofi’s mother, meanwhile, said Monday that she couldn’t imagine what went through the mind of her son.

Sharon Soofi said her son was always deeply religious, but she never thought he would hurt anyone, reports CBS News correspondent Omar Villafranca.

“He was a practicing Muslim, but not in the extreme sense,” Soofi said. “He just tried to make people understand Islam.”

Authorities said Soofi, 34, and Simpson, 30, arrived Sunday at the Dallas-area community center armed with body armor, assault rifles and a mission.

Clearly Soofi had been radicalized, with all due respect to his mother, who pointedly did not issue denials or defenses of her son. The premeditation was clear in the preparations. Both men wore body armor and carried weapons. As the police spokesman says, “they were [both] there to shoot people.”

The ISIS claim here seems a little dodgy. Simpson’s destination in 2010 was Somalia, not Syria, which would perhaps put him more on the roster of aspirational members of al-Shabaab rather than ISIS. It doesn’t mean that Simpson couldn’t have switched allegiances in the following years, though, and it certainly doesn’t preclude the possibility that he joined ISIS and took orders from the terrorist army. The FBI will be scouring his communications and his residence for any evidence of that. It’s pretty easy to make this kind of claim after the fact, though, and it would not be surprising if Simpson turns out to be another “known wolf” self-starter.

If it does turn out that ISIS ran Simpson as a kind of sleeper agent — more like a stringer, given his profile with US law enforcement — it will heighten the issue of the prevention of domestic attacks. Either way, it’s clear that this was a terrorist attack on US citizens exercising their right to speak in public. Perhaps this claim will put this in proper perspective, rather than continuing to blame intended victims like Pamela Geller and Geert Wilders for the attack.