Former German spy chief August Hanning was detained on Tuesday on suspicion of attempted treason in a case that ranks among Germany’s biggest intelligence scandals since the Cold War.

Prosecutors accused him of paying for secret documents and using them in an analysis for a foreign spy service. They did not identify the intelligence service and it was not immediately clear whether the analysis reached its intended recipient.

The arrest of a former head of Germany’s foreign intelligence is unprecedented and could damage the country’s intelligence relationships with allied nations, according to a senior security lawmaker.