I didn't find the Count Marco letter listed in either list of letters.
This one to me is a very interesting letter.
It was signed the Red Phantom ( red with rage ). Some people have found that there was a Red phantom who was a well known wrestler from way back in the 1920's I think. They felt that this was what the Zodiac was emulating.
From the first time I saw the Red Phantom letter I thought of the Green Phantom from the late 60's. He was a mysterious person ,who would leave a bottle of Scope mouthwash for people with bad breath.
Along with the bottle of "Scope", he would leave a note letting the people know the Green Phantom was there, urging the recipient to use the mouthwash ! T
these people would do their best to unmask the offending Green Phantom.
As we know there was a connection to southern California and the Zodiac. I found this while looking for a reference to the green Phantom, someone had found hidden behind several layers of wall paper, a note written on the wall.
The note read : Help ! The Green Phantom stole my Listerine !
I Googled Scope mouthwash TV adds. and found -----"If The Walls could talk". I think that if you can find this printing on the wall ,you will get a chill . It looks very much like the Z's printing ! Sorry I don't know how to give links.