The Zodiac Killer appeared to commemorate anniversaries and dates, such as the Lake Herman Road murders and Melvin Belli letter on December 20th 1968 and 1969 (possibly with the release date of the 1965 movie The 10th Victim). He mailed the Pines card on March 22nd 1971 referring to the abduction of the missing Donna Lass, exactly one year after the abduction of Kathleen Johns on Highway 132. He mailed the 1987 "Halloween" letter seventeen years after the 1970 Halloween card. The March 13th 1971 "Los Angeles" letter was mailed on the US release date of the Vanishing Point movie, which used the same language as the letter in its January trailer..The August 1st 1973 "Albany" letter was mailed in response to a recent newspaper article that featured the date of August 1st 1969, by mentioning the receipt of the Zodiac Killer's first three letters and cryptograms. The "Albany" letter also carried another cryptic offering. One could argue that these are just coincidental. But if they were not, what anniverary or date could have inspired the Zodiac Killer to select a Groucho Marx Christmas card in 1990, which he may have had to source in advance to ensure his selected choice.