In Town X, a burglary is reported to the police. They investigate, and their investigation leads to Bob, who has previous convictions for that sort of thing. They find the stolen goods at Bob's house, Bob is questioned, he confesses, it goes to trial, Bob pleads guilty, the jury is convinced by the evidence, and Bob is sentenced accordingly.
In fact, Bob had not committed the burglary. In fact, he had a provable alibi - he was out committing another burglary (of equivalent severity) elsewhere in town at the time. The original burglary was done by a friend of his, and he was just storing the goods at his house. Given that demonstrating his alibi wouldn't have saved him any prison time, and would have involved fingering his accomplices (which would have damaged his standing in the criminal underworld), he felt that the simplest thing to do was to take the rap for the original burglary.
This is all to illustrate a philosophical point about the word "know" (and "knowledge" etc). A poll:
Note that the previous convictions don't count when I'm asking whether the legal system knew Bob had committed burglary... I meant to ask "...committed burglary on that day" or something similar. This ETA is before anyone but me has answered this, so all the results reflect this ETA)( poll under cut )