The BBC reports that a father, concerned about his under-age daughter's relationship with an adult ice hockey coach, installed spy software on the family PC to monitor her online liaisons. It soon became apparent from the emails and Messenger chat the pair were exchanging that they were having unlawful sexual intercourse. The coach was arrested, charged and convicted of five counts of sexual activity with a child and jailed for 4½ years.
In a corporate setting, it is not entirely obvious to many IT, HR and information security professionals whether an employer has the legal right to monitor it's employees' use of email and other IT facilities in the same way, even if those facilities clearly belong to the organization and are provided to employees for work purposes. In some countries, privacy laws constrain what employee monitoring employers can reasonably do but there are often exceptions to permit more intrusive monitoring in order to investigate suspected illegal activities - not random interception, perhaps, but targeted monitoring of specific individuals which the organization has good reason to believe are doing something illegal. There may be further exceptions in relation to serious crimes such as pedophilia, allowing organizations and law enforcement to present pretinent information obtained by chance as evidence in court, even though they had no prior knowledge of the crime. [NB: this is not legal advice! I am not a lawyer! Consult a competent lawyer familiar with the laws in your country to find out what you can and cannot do.]