Relevancy of statements: signed responses to summons may be admissible in prosecutions when declarant unavailable or admitted. Section 136 provides that a signed statement made in response to a summons under section 70 is admissible in prosecution to prove its contents when the declarant is unavailable (dead, cannot be found, incapable, kept away, or cannot be produced without unreasonable delay or expense) or when the declarant is examined as a witness and the court admits the statement in the interest of justice.