Legal Jargon (in Britain at least) for "Taken into Consideration". Basically a criminal admits to crimes that he wasn't originally arrested for. This means that he can wipe his slate clean (of those ones at least), while the punishment is lumped into the sentance he is serving for the 'original' crime, usually quite lenient (as a reward for going guilty). Can be used to demonstrate remorse. By accepting a definite small punishment now, he doesn't have to worry about the chance of a more severe sentence later if the crime was solved 'normally'.
The leniency encourages the closure of unsolved crimes.