1-5-302: When execution may be proved by handwriting.

The execution of an instrument may be established by proof of the handwriting of the party and of a subscribing witness, if there is one, in the following cases:

(1) when the parties and all the subscribing witnesses are dead;

(2) when the parties and all the subscribing witnesses are nonresidents of the state;

(3) when the place of their residence is unknown to the party desiring the proof and cannot be ascertained by the exercise of due diligence;

(4) when the subscribing witness hides or cannot be found by the officer by the exercise of due diligence in attempting to serve the subpoena or attachment; or

(5) in case of the continued failure or refusal of the witness to testify for the period of 1 hour after the witness's appearance.