“What this tells me is that whoever leaked this is not very tech savvy,” he said.

The Tor network functions as a sort of Internet maze to throw off anyone who tries to trace the origin of an electronic message, Mr. Meinrath said. When the network receives a message, it bounces from server to server. The ordinary Internet pastes a series of addresses onto a message, allowing it to be traced back to the sender. In contrast, the Tor network strips that information out.

When the message emerges from the network, the source is, in theory, untraceable. Even so, it has long been known that intelligence and law enforcement agencies have made extensive efforts to infiltrate the Tor network and trace those who use it.

Many of the servers on the Tor network are run by volunteers. Mr. Meinrath said that if the F.B.I. explored the network, it was possible that investigators were not able to infiltrate enough servers on their own to trace the origin of the documents.

“Probably the F.B.I. had some of that information but not all of it,” Mr. Meinrath said.

Another possibility, he said, was that the volunteer was not operating a server properly and kept information about the routes taken by the messages passing through it.

A skilled hacker, Mr. Meinrath said, would take into account all of these possibilities and add one or two additional layers of security to the communication — for example, using software to cloak the identity of the computer that sent the message and connecting to the Internet somewhere that could not be linked to its source. Those measures seem to have eluded those who did the hacking.