ZKS Handwriting.....the big one
On July 31st 2013 traveller1st provided a detailed examination of the Count Marco and Badlands letters in terms of handwriting characteristics and provides an in depth analysis of letter formation.
Initial viewing of the two letters side by side seems inconclusive, particularly considering the style of the letter C. However this forum post may change your mind.
Both the Badlands and Count Marco letters were mailed in succession of each other, in May and July of 1974, and as such, are regarded as the more questionable of the Zodiac Killer correspondence.
Nevertheless this forum thread is an interesting read and may challenge some of your widely held beliefs. Visit thread here.