RCW 11.20.070
Proof of lost or destroyed will.
(1) If a will has been lost or destroyed under circumstances such that the loss or destruction does not have the effect of revoking the will, the court may take proof of the execution and validity of the will and establish it, notice to all persons interested having been first given. The proof must be reduced to writing and signed by any witnesses who have testified as to the execution and validity, and must be filed with the clerk of the court.
(2) The provisions of a lost or destroyed will must be proved by clear, cogent, and convincing evidence, consisting at least in part of a witness to either its contents or the authenticity of a copy of the will.
(3) When a lost or destroyed will is established under subsections (1) and (2) of this section, its provisions must be distinctly stated in the judgment establishing it, and the judgment must be recorded as wills are required to be recorded. A personal representative may be appointed by the court in the same manner as is herein provided with reference to original wills presented to the court for probate.
