Hmmm, I don't think, if the allegations/accusations were "serious enough" that if (actually having never used the personal devices for work) someone had replied

Hmmm, I don't think, if the allegations/accusations were "serious enough" that if (actually having never used the personal devices for work) someone had replied "No, never" they would have taken your word as good, i.e. they would have probably said "OK, now let's check if that is true" and confiscated the devices as well. Please also understand that when you say "No, never" to a FBI agent, you myst be pretty sure that it is accurate, as if they (still hypothetically) find even a single interaction they could accuse you to lying to a government officer. Anyway, yours is the right approach, never, and I mean never mix personal with work relatd activities.