Noting that other experts have claimed that the information contained in the latest documents checks against data they have on individuals, he suggested that the formatting may have been altered. “Perhaps it’s a case of raw data which is authentic, and in order to make it more desirable it was dressed up,” Mr. Winter said.

Germany hopes that information from the documents can serve as evidence in the trials of several citizens facing charges related to terrorist activities, Interior Minister Thomas de Maizière told reporters on Tuesday.

“They offer a great chance to provide evidence and to prove that Germans took part in terrorist activities of the so-called Islamic State,” Mr. de Maizière said of the documents. “We will be able to better prove these activities, speed and better clarify our investigations, and come to stronger sentences.”

Membership in a terrorist organization is a criminal offense in Germany, but the authorities in the past have had a hard time proving that even someone who admitted to having been in Syria actually took part in fighting for the Islamic State, also known as ISIS or ISIL. A suspect currently standing trial in a Frankfurt state court on charges of illegal weapons possession and plotting an attack on a sovereign state — he is identified only as Abdulkarim B. in keeping with German privacy laws — was among those on the lists seen by Süddeutsche Zeitung, NDR and WDR, they said. If so, prosecutors would be able to press charges of membership in a terrorist organization.

Sky News reported the documents include information about 22,000 foreigners from 51 countries, including Britain and the United States. Recruits were also asked to give their blood types, mothers’ maiden names and “level of Shariah understanding,” among other information, Sky News said.

Prospective members were also asked whether they wanted to serve as fighters or as suicide bombers, the German news media reported.