Authorities in both the U.S. and the United Kingdom were by that time aware that a spy ring was operating out of New York City. The first break came when "British Imperial Censorship", located in the Princess Hotel in Bermuda and run by the British Security Coordination (BSC) — actually a cover for the Secret Intelligence Service — intercepted a letter written to "Lothar Frederick" and signed by a "Joe K". As it was known that "Lothar" was an alias used by Heydrich, a watch was set for any letter with the Joe K signature. Subsequent letters from Joe K were intercepted, their contents read and recorded, and the envelopes so carefully resealed that their recipients would not detect any evidence of tampering.