Surveillance changes people
In Germany a survey was held to investigate how the data retention policy on email, phone and mobile communication influences ones behaviour. The survey shows that many Germans don’t use phone and mobile for most confidential contacts anymore. These contacts have nothing to do with crime but with confidential stuff like marriage- or drugs counseling. Here is a clear indication that data-retention changes people. People under surveillance behave differently that people who are free.
Needless to say that people with bad intentions are not using these forms of communication anyway so this doesn’t help in fighting crime. Data-retention is useless.