Smiddy - Is it not a criminal offence to know about a crime and not report it to the police / Law /authorities ?
Yes it is, or was, a criminal offence. In English common law it is called "misprison of felony". Here is a wikipedia link explaining it:
The link says the offence has been abolished in NSW, "and other Australian States and Territories". However, I am pretty sure that it survives in at least one major Australian State.
The offence itself is only a misdemeanor. At a guess, the reason we haven't heard of any prosecutions may be that there are statute of limitations issues, or that misdemeanor convictions don't often get reported in the newspapers.