 He was honorably discharged in 1971.Penn's writing, mostly focused on the Zodiac case, was largely published in "The Ecphorizer", the newsletter of the San Francisco chapter of Mensa International, which had a peak readership of 700 and was published between 1981 and 1995 A 1972 piece he wrote while attending UC Berkeley, "Gottfried von Strassburg and the Invisible Art" was published in the peer-reviewed journal of Germanic studies Colloquia Germanica.The piece is a reflection on the legend of Tristan, a 12th-century hero of Celtic folklore.