Other than the right to do business as a Private Investigator in the State of Washington as granted by the SOS and regulated by the DOL and DOR, PIs have NO powers above any other regular citizen.
In no way shape or form do private Investigators have any powers or authority provided to Law Enforcement Officials. It is unlawful for a private investigator to represent themselves as a Law Enforcement official by any means. An Armed Private Investigator may not display a firearm while soliciting clients.
Only Laywers have client privilege. Those privileges may extend to Private Investigators if the investigator is working for a Lawyer on a case that is privileged.
No powers of arrest beyond what any other citizen has.