Does an Insurer have a duty to investigate an accident?

The accident was in WA state.

I understand that they do have a duty to investigate

Specifically not to the insurer but, do they have a duty to investigate to a tortfeasor or uninsured driver?

I am looking for legal grounds to dispute a case which involves a botched investigation by the insurer. I fully plan to have a meritorious defense but would like to fault the Insurer of the other party.

As I was uninsured at the time.