The DOJ arrested 25-year-old Reality Leigh Winner and accused her of mailing sensitive documents to a news outlet. The department's description lines up with a classified report on Russian election interference leaked to The Intercept.
Investigators said they narrowed down the suspects after they noticed crease marks on the leaked documents, which indicated "they had been printed and hand-carried out of a secured space."
The documents published by The Intercept did have crease marks. But they also had something else: Each page was covered in a matrix of nearly-invisible yellow dots.
Security researchers say those dots can identify when and where these documents were printed out. That'd make it pretty easy to pinpoint Winner as the leaker.
The Intercept says it doesn't know who sent it the NSA documents, but it characterized the government's story of Winner's arrest as "speculation designed to serve the government’s agenda."