The tidbit was passed on by Clive Goodman to Andy Coulson, then editor of the now-defunct News of the World.
Goodman's 2005 email notes: "memo (has) now gone around to all palace cops telling them to keep their sticky fingers out."
The email was used as evidence at the phone-hacking trial of Coulson, former editor Rebekah Brooks and five others. All deny guilt.
An eighth defendant, Ian Edmondson, was dropped from the trial Thursday because doctors have declared him unfit to stand trial. Judge John Saunders said Edmondon would be tried once he has recovered.