Chancellor Angela Merkel has repeatedly said she knew nothing about American surveillance activities in Germany. But documents seen by SPIEGEL show that German intelligence cooperates closely with the NSA and even uses spy software provided by the US.

It was a busy two days for the surveillance specialists of the Bundesnachrichtendienst (BND), Germany's foreign intelligence agency. At the end of April, a team of 12 senior BND officials flew to the United States, where they visited the heart of the global American surveillance empire: the National Security Agency (NSA). The purpose of their mission can be read in a "top secret" NSA document which SPIEGEL has seen -- one of the trove of files in the possession of whistleblower Edward Snowden.

According to the document, BND President Gerhard Schindler repeatedly expressed an "eagerness" to cooperate more closely with the NSA. The Germans, the document reads, were looking for "guidance and advice."