It stated that on March 13th 1978 at 2300 hours (just over a month before the "I am back with you" letter) somebody made a sinister phone call to an individual living in the Mission District of San Francisco, whose home voice recorder had stored the message. Apparently David Toschi responded to this incident. When played, the message read "This is the Zodiac. Tell the press I am back in San Francisco". The reportee stated he has no idea why the call came to him. Over four years had elapsed since the January 29th 1974 Exorcist letter, yet here we have a malicious phone call from somebody claiming to be Zodiac with the words "I am back", just over a month before the April 24th 1978 letter mailed to the San Francisco Chronicle stating "I am back with you". Another comparison between the two is "Tell the press I am back" and "Tell herb caen I am here". Both concerning the newspapers. Herb Caen was a San Francisco humorist and journalist whose daily column ran in the San Francisco Chronicle for nearly sixty years.
On May 5th 1978, just 11 days after the "I am back with you" letter, somebody claiming to be the Zodiac Killer phoned the San Mateo Police Department and falsely reported that a bomb had been set in the Transamerica building at 600 Montgomery Street (the same street of Melvin Belli's residence in 1969). Although it is difficult to separate the hoaxers from the real Zodiac Killer, we do have the common phraseology in the voice recording and letter on March 13th and April 24th 1978, that while not compelling, is nonetheless interesting.