A person commits a class B felony if, believing that an official proceeding, as defined in RSA 641:1, II, or investigation is pending or about to be instituted, he:
I. Alters, destroys, conceals or removes any thing with a purpose to impair its verity or availability in such proceeding or investigation; or
II. Makes, presents or uses any thing which he knows to be false with a purpose to deceive a public servant who is or may be engaged in such proceeding or investigation.