There's no implication that the source is necessarily illegal.
Let's imagine a more traditional wiretap scenario. Say the police are gathering information on a major drug kingpin, and they need more information from him.
But they want to bring in one of his lieutenants because of information they've found on the wiretap. It'd make plenty of sense to find a way to bust the lieutenant without making the existence of the wiretap public.
It's not really about "laundering" evidence, in this case. Though it could very easily be used that way, since the actual source of the actions is hidden. The original wiretap could have been perfectly legal.
Let's imagine a more traditional wiretap scenario. Say the police are gathering information on a major drug kingpin, and they need more information from him.
But they want to bring in one of his lieutenants because of information they've found on the wiretap. It'd make plenty of sense to find a way to bust the lieutenant without making the existence of the wiretap public.
It's not really about "laundering" evidence, in this case. Though it could very easily be used that way, since the actual source of the actions is hidden. The original wiretap could have been perfectly legal.