The discovery of a laptop purportedly belonging to a member of the Islamic State is raising new questions about whether the terrorist group, which U.S. officials say is more dangerous than al Qaeda, is poised to launch an attack using weapons of mass destruction.

U.S. officials and terrorism experts said that the discovery of the laptop by Foreign Policy Magazine, lifted from a Syrian rebel fighter, raises troubling questions about the Islamic State’s intentions and its ability to conduct a WMD strike.

However they said the presence documents on building biological weapons does not necessarily add up to an actual capability to use them.

“I wouldn’t dismiss the idea of a WMD attack by terrorists,” said Daveed Gartenstein-Ross, a senior fellow with the Foundation for Defense of Democracies told FP. “It’s something we should guard against. But in terms of something I worry about, it’s far down the list.”

More than 35,000 files were found on the laptop, offering some of the most precise information to date on the Islamic State’s WMD aspirations.

The laptop, which was examined by correspondents for Foreign Policy, contains thousands of files related to planning and launching terrorist attacks. Most troubling is a document that discusses how to weaponize bubonic plague. But turning that knowledge into a working weapon requires particular expertise, and it’s not clear that the Islamic State has it.

“That they have the capabilities and intentions [to build some WMD] is beyond dispute,” Gartenstein-Ross said.

FP Magazine reported that the Islamic State would still face considerable obstacles if it actually attempted to build a weapon with bubonic plague. “It’s a very dangerous thing to try to harness as an offensive weapon, in part because you might kill all your own guys in the process,” Gartenstein-Ross said.