Key differences between Islamic State's claim of responsibility for the New York City truck attack and claims for previous terror attacks have caught the eye of counterterror officials, who are trying to determine what it might mean for the state of terror group.
Most notably, they said, the way in which IS issued the claim failed to follow the group's usual patterns, raising questions about whether the collapse of the group's self-declared caliphate in Iraq and Syria was starting to take a toll.
"One of the soldiers of the Islamic State attacked a number of crusaders on a street in New York City," the group's weekly al-Naba newsletter said late Thursday, claiming attacker Sayfullo Saipov, 29, as one of its own.
"This is one of the most prominent attacks to target crusaders in America," al-Naba continued, adding, "[By] the grace of Allah, the operation instilled fear in crusader America."
But officials and analysts said that it's rare for IS to make such a claim first in al-Naba.
"It's not unprecedented, but it is something we're not used to," said Raphael Gluck, an independent researcher.
While considered an official IS channel, al-Naba has traditionally been used to follow up on the group's initial claims, which often come from its Amaq or Nashir news agencies, in multiple languages, via social media.
Relying on those news agencies this time, however, may not have been possible.
"The Amaq news agency has sputtered in recent weeks, and struggled without a website," Gluck said.
There are also questions about how the statement in al-Naba was worded, which also differs from wordings in many previous claims.
"The al-Naba story on the New York attack relies exclusively on outside media reporting of the attacks," according to an analysis done by Ryan Pereira for the Counter Extremism Project.
"Traditionally, Amaq and al-Naba claims for responsibility include language suggesting that a source close to Amaq or a source close to the Islamic State relayed attack details to the group's media officials," Pereira wrote.
Nor did the account in al-Naba offer any evidence to substantiate the group's claim.
Additionally, it has been rare, though not unprecedented, for IS to claim an attacker as a "soldier of the caliphate" if he is still alive.
Another part of the al-Naba statement that caught the attention of counterterror officials was the way it referred to the deadly October 1 shooting in Las Vegas that killed 58 people and wounded hundreds more.
Al-Naba described the Las Vegas shooting as "the attack carried out by the mujahid brother Abu Abdul Barr al-Amriki — may Allah accept him — against a large gathering of crusaders."
It was not the first time IS had claimed the Las Vegas shooter, Stephen Paddock, 64, as one of its own, referring to him with an Arabic nom de guerre. But so far, investigators have yet to come forward with any evidence that connects him to IS.
Instead, U.S. counterterror officials have cautioned for months that IS is increasingly opportunistic, even desperate, with one official noting the group has been "stepping up its claims of inspired attacks even in cases that do not appear to be connected to the group."
And, although they admit IS has been been able to adapt to losses and hardships, some see the claim late Thursday for this week's attack as possibly falling along those lines.