From Charles Turchick of the "Minnesota 8":

I think this is the statute we originally were charged under, although it may have been changed since then. The word "sabotage" doesn't appear here, but it is part of the "Sabotage Act" https://criminal.findlaw.com/criminal-charges/sabotage.html

"Section 2155. Destruction of national-defense materials, national-defense premises, or national-defense utilities

"(a) Whoever, with intent to injure, interfere with, or obstruct the national defense of the United States, willfully injures, destroys, contaminates or infects, or attempts to so injure, destroy, contaminate or infect any national-defense material, national-defense premises, or national-defense utilities, shall be fined under this title or imprisoned not more than ten years, or both.

"(b) If two or more persons conspire to violate this section, and one or more of such persons do any act to effect the object of the conspiracy, each of the parties to such conspiracy shall be punished as provided in subsection (a) of this section."

Then in another portion of the U.S. Code, there are definitions that relate to "sabotage" and "international terrorism." http://www.law.cornell.edu/uscode/html/uscode50/usc_sec_50_00001801----000-.html Those definitions include ones for "foreign power" and "agent of a foreign power." Who knows where those definitions were 40 years ago, but maybe (Prosecutor Robert) Renner made references to an international conspiracy and to Castro to make the offense fit the sabotage act of the time.