According to an affidavit filed in a related case last week, Elton Simpson — one of two men who donned body armor and fired assault weapons before being shot dead by a Garland police officer — had been corresponding with an undercover FBI agent. And in a text message roughly a week before the attack, as they discussed the cartoon contest, the agent had exhorted Simpson to “Tear up Texas.”

The revelation that an undercover FBI agent encouraged a would-be terrorist to “Tear up Texas” shortly before he opened fire on a “Draw Muhammad” cartoon contest in Garland, Texas, last year raises new concerns about FBI counterterrorism efforts that were already under fire for manufacturing terrorism cases rather than halting them.

The FBI, in the affidavit, explained the comment as “an effort to continue their dialogue” with the suspect.

But testing the willingness of suspects to take certain steps in a conspiracy is one thing; actively encouraging them to commit a violent, criminal act is another.

“The FBI uses informants and undercover agents to pressure suspected ISIS sympathizers into committing acts of violence, so that they can then be prosecuted. The Garland shooter case is the most striking illustration yet of the dangers of this approach,” says Arun Kundnani, a lecturer on terrorism studies at New York University. “Essentially, it suggests the government may be manufacturing the very threat it is supposed to be countering.”

Kundnani called for “an independent congressional investigation of the FBI’s tactics.”

The extensive role played by the undercover agent was first reported by the Daily Beast.

Though sting operations are generally seen as an appropriate tool for infiltrating criminal organizations or conspiracies, their use is more problematic in contemporary terrorism cases involving isolated individuals. In those cases, the concern is that the informant or undercover agent could plant the idea to actually conduct an attack in the mind of a suggestible or unstable person.

“These cases always have a lot of gray area and there has always been a question of how far the FBI should go when they get involved in these sting operations,” said Karen Greenberg, director of the Center on National Security at Fordham Law School. “But if you’re going to target potentially unstable, vulnerable individuals in undercover sting operations, you have to examine the potential consequences of having these types of discussions with them.”

The utility of sting operations has changed in the era of Islamic State, Greenberg said. Terrorist groups in the past, including al Qaeda, tended to have more coherent plots and mature conspirators. “There are several factors which make it harder to control a situation with informants in ISIS cases, including the instability, vulnerability, and, frequently, the young age of most ISIS recruits,” Greenberg said. “Not only is there often a lack of a specific plot in mind, there tends to be a real sense of suicidal thinking and self-hatred in their motivations that can make it more difficult to control a situation.”

“We just don’t know what happened in this case, but it’s a real warning sign that the foreseeable consequences of acts are now unknown,” she adds. In none of the previous cases is the FBI known to have actively encouraged violence, nor dealt with anyone equipped and prepared to carry out an imminent, violent act. Here they seemingly did both.

FBI Director James Comey has said there are active investigations of suspected ISIS sympathizers ongoing “in all 50 states.” But little is known about the nature of the individuals held under suspicion or what methods the FBI is using to investigate them.

The New York Times reported in June that since February 2015, two thirds of terrorism prosecutions related to Islamic State have involved undercover operatives.

And in recent years a number of plots have materialized involving seemingly unstable individuals interacting with government informants. This January, a 25-year-old man with a history of psychiatric problems was arrested after attempting to attack an upstate New York bar with a machete — with the assistance of a government informant who helped provide him with the machete. And in October 2014, a former army recruit was introduced to FBI informants after being released from of a mental institution. Months later, he was arrested for plotting to attack a military facility — with a fake bomb provided by the informants.

Although more than 100 alleged Islamic State plots have been documented in the United States since 2014, it’s unclear how many would have materialized without the involvement of informants or undercover agents. Such cases nevertheless help inflate the public fear of terrorism and feed the misconception that terrorist sleeper cells are ubiquitous in the United States.

The escalation of FBI tactics to actively encouraging violent actors in these investigations would be a dangerous step.

Many of the targets of prior terrorism investigations did not demonstrate any ability to prepare for an actual attack without the FBI providing their equipment. But the Garland shooters did.

And had they been more competent in their assault, the result could have been one of the deadliest terrorist attacks in recent U.S. history – an attack that was encouraged by the FBI.