(1) A witness or a person believing he is to be called as a witness in any official proceeding commits a class 4 felony if he intentionally solicits, accepts, or agrees to accept any benefit upon an agreement or understanding that:
(a) He will testify falsely or unlawfully withhold testimony; or
(b) He will attempt to avoid legal process summoning him to testify; or
(c) He will attempt to absent himself from an official proceeding to which he has been legally summoned.