Texas Attacker Left Trail of Extremist Ideas on Twitter

Counterterrorism officials on Tuesday were studying the electronic trails left by two men killed by a police officer as they shot at a Prophet Muhammad cartoon contest in Texas, looking for any direct ties to the Islamic State extremist group in Syria. The group praised the gunmen in a statement as “soldiers of the caliphate,” the unified Muslim land that it purports to be building.

But any secret ties that officials might find may be less important than the public exchanges of messages on Twitter by one of the gunmen, Elton Simpson, in the weeks before the attack. Mr. Simpson, a convert to Islam with a long history of extremism, regularly traded calls for violence on Twitter with Islamic State fighters and supporters, as well as avowed enemies of Pamela Geller, the organizer of the cartoon contest.

His Twitter contacts included Junaid Hussain, a British fighter with the Islamic State in Syria known as Abu Hussain al-Britani, and Mohamed Abdullahi Hassan, a Somali-American now in Somalia who uses the name Mujahid Miski and frequently promotes the Islamic State. Both men called for violence, and Mr. Hassan had suggested the Texas event as a possible target.

On April 23, 10 days before the Texas attack, Mr. Hassan linked to the planned cartoon event in Texas, praised the January shootings at a satirical newspaper in Paris and called on jihadists in the United States to follow that example.

“The brothers from the Charlie Hebdo attack did their part,” Mr. Hassan wrote in the post. “It’s time for brothers in the #US to do their part.”

Later the same day, Mr. Simpson posted about the cartoon contest, using the handle Shariah is Light: “When will they ever learn. They are planning on selecting the best picture drawn of Rasulullah (saws) in Texas.” Rasulullah (saws) is a respectful phrase for the prophet.

The onslaught of recruitment propaganda has multiplied the number of online enthusiasts for the Islamic State in the United States, giving counterterrorism investigators the difficult task of deciding which are simply fantasizing in public and which might be planning violence.

“The ISIS guys are talking to these wannabes on Twitter all day long,” a senior law enforcement official said. “It’s like the devil is sitting on their shoulder saying, ‘Come on, they’re insulting the prophet, what are you going to do about it?’ ” The official, who would speak about the continuing investigation only on condition of anonymity, said that although Mr. Simpson had long been under F.B.I. scrutiny, he had not appeared to be preparing for violence.

“There are so many like him that you have to prioritize your investigations,” the official said. {snip}

{snip}

Several months ago, after Mr. Simpson began posting on Twitter about the Islamic State, the F.B.I. and the police in Phoenix opened a new investigation, officials said. As part of that inquiry, the authorities monitored his online postings and occasionally put him under surveillance, the officials said. Mr. Soofi was not under investigation.

{snip}

Yet with dozens, or perhaps hundreds, of people across the United States expressing online sympathy for the Islamic State, authorities are unable to keep them all under physical surveillance or track them online. Watching a single suspect night and day can require a team of 25 people in shifts around the clock.

{snip}