Relevancy of statements under summons: admissible in prosecution when maker is unavailable or court admits in interest of justice. Section 136 renders a signed statement made on appearance to a summons under section 70 admissible in prosecutions under the Act to prove the truth of its contents when the maker is unavailable (dead, cannot be found, incapable, kept away by an adverse party, or presence would cause unreasonable delay or expense) or when the maker is examined as a witness and the court permits admission in the interest of justice.