- they're able to investigate whether the regulators did their job properly in regulating, while being organisationally at least somewhat distant from the regul

- they're able to investigate whether the regulators did their job properly in regulating, while being organisationally at least somewhat distant from the regulator they're looking at (obviously they tend to maintain close relationships with the appropriate regulators but at least they're not literally in the same building) - people will be more willing to talk to investigators if they know that their evidence won't be used against them in court or used for a licence suspension - you can grant non-regulatory investigators greater powers to compel testimony and documentary evidence, perhaps even if it's self-incriminating (I can't speak for the US but it's common here in Australia where we don't have a 5th Amendment entrenched guarantee), without running into as many ethical issues as when you give coercive information-gathering powers to regulators - you ban such compelled testimony from being used as evidence in court or in regulatory proceedings - you don't need as high a standard of proof to make an investigatory finding as if you're taking punitive action against a specific individual - the overall purpose of the investigation is aimed at systemic safety, rather than getting a successful prosecution None of this prevents the regulators from running a parallel investigation with the aim of regulatory punishment - and indeed, two sets of independent eyes on complex scenarios is good too.