Relevancy of statements: signed responses to summons may be admitted when the declarant is unavailable or court permits in interest of justice. A signed statement made on appearance in response to a summons issued during an inquiry is admissible to prove its contents in a prosecution when the declarant is unavailable (dead, cannot be found, incapable of giving evidence, concealed by an adverse party, or where obtaining presence would cause unreasonable delay or expense), or when the declarant is examined and the court, considering the circumstances, admits the statement in the interest of justice.