"Paul Avery and Kate Coleman who wrote the sizzling expose of Black Panther violence in the July 10th New Times 'have gone out of the area' after receiving the predictable threats," wrote Herb Caen. The bogus letter reopened old wounds, driving the populace to seek closure on the long-unsolved case. Zodiac tips quadrupled. "The Zodiac was shot to death by San Francisco police in March of 1976," a reader informed Caen, "about four months after he set the Gartland Hotel fire that killed thirteen people." Zodiac Unmasked. 
​
On July 19th 1978 a typewritten letter from Los Angeles arrived at the San Francisco Chronicle stating:
"I am the ZODIAC and I am in control of all things. I am going to tell you a secret. I like friction tape. I like to have it around in case I need to truss someone up in a hurry....I have my real name on a small metallic tape. You see, while you have it in your possession, I want you to know it belongs to me and you think I may have left it accidentally. I am athletic. It could be swim fins, or a piece of scuba gear. But maybe you play chess with me. I have several cheap sets in closets all over. I have my name on the bottom of the lid with the scotch tape....My tape is waiting for me all over California. Do you know me? I am the ZODIAC and I am in control."  

Sergeant John Lynch from the Vallejo Police Department interviewed Arthur Leigh Allen, with Allen stating that he traveled to Salt Point Ranch, located on the coast, due west of Napa on September 26th 1969 for a spot of scuba diving.
Clearly, Arthur Leigh Allen was a prime suspect for Zodiac, so it must have been obvious to Allen that he would incriminate himself by inserting "swim fins" and "scuba gear" into the narrative of the 1978 letter, unless you believe a double bluff. 
This letter followed the "I am back with you" correspondence mailed to the San Francisco Chronicle on April 24th 1978, just three months earlier.
Arthur Leigh  had been released from the Atascadero State Hospital on August 31st 1977, and this letter is often touted as his return to the persona of the Zodiac Killer after a lengthy  absence. Or was it more likely that somebody known or unknown to Allen was attempting to implicate him in the murders by dropping subtle clues pointing in his direction. 
The author of the July 1978 letter seemingly wants to push us in the direction of tape: "I like friction tape", "I have my real name on a small metallic tape," "I have my name on the bottom of the lid with the scotch tape," and "My tape is waiting for me all over California​." 
It appears like a selling job, trying to push the tape angle in connection with trussing people up, whereas the author may have had other intentions.

The Zodiac Killer mailed us a 'Bus Bomb' diagram on November 9th 1969 and April 20th 1970 employing the use of electrical circuits.
'Friction tape is a type of adhesive tape made from cloth impregnated with a rubber-based adhesive, mainly used to insulate splices in electric wires and cables. Because the adhesive is impregnated in the cloth, friction tape is sticky on both sides. The rubber-based adhesive makes it an electrical insulator and provides a degree of protection from liquids and corrosion. In the past, friction tape was widely used by electricians, but PVC electrical tape has replaced it in most applications today. The frictional properties of the tape come from the cloth material, which is usually made from cotton, while the fabric base protects electrical splices against punctures and abrasion. Wikipedia.' 
Was this the implication, with 'pipe bombs' having been discovered at Allen's residence, along with supposed bomb manuals.
But more credible, is the emphasis on "swim fins" and "scuba gear," considering Allen's penchant for scuba diving, and the opportunities for such pursuits provided by Lake Berryessa, Lake Tahoe and Fisherman's Wharf near to the Presidio Park- in three Zodiac linked crimes. 
Permanent marker pens, in conjunction with water resistant tape or labels are ideal for scuba divers and boat enthusiasts, for personalizing your equipment. dolphindiveathens.com/marking-your-dive-gear/. "I have my name on the bottom of the lid with the scotch tape....My tape is waiting for me all over California."
With Arthur Leigh Allen the prime Zodiac candidate for many years, isn't it plausible that somebody was attempting to throw Allen under the proverbial 'school bus' in an attempt to keep him in the frame, while keeping an interest in the Zodiac case burning bright. These two letters could actually be from Zodiac (depending on the validity of DNA evidence), and is simply a game by the real killer to keep the spotlight firmly focused on his convenient "fall guy."​

'I keep on hearing the police have caught me but they wont fix me just yet. I have laughed when they look so clever and talk about being on the right track'. Taunting words dragged from the 'Dear Boss' letter, presumably sent by Jack the Ripper and mailed on September 27th 1888, exactly 81 years prior to the Lake Berryessa attack on Bryan Hartnell and Cecelia Shepard. In this letter he taunts the police 'The next job I do I shall clip the ladys ears off and send to the police officers just for jolly wouldn't you. Keep this letter back till I do a bit more work, then give it out straight. My knife's so nice and sharp I want to get to work right away if I get a chance. Good Luck. Yours truly. Jack the Ripper'.
Bearing in mind the wording on the Ripper letter, the 'next job' the Zodiac Killer undertook after the Lake Berryessa attack was the murder of Paul Stine, in the wealthy district of Presidio Heights on October 11th 1969. Despite the callousness of the crime, the Zodiac Killer did refrain from the unthinkable, although he did remove an item from the crime scene, tearing off a section of Paul Stine's shirt and sending it to authorities. Two days after the murder, this letter, not dissimilar to the 'Dear Boss' letter, arrived at the San Francisco Chronicle on October 13th 1969. It said 'The S.F. Police could have caught me last night if they had searched the park properly instead of holding road races with their motorcicles seeing who could make the most noise. The car drivers should have just parked their cars and sat there quietly waiting for me to come out of cover'.
He then backed this up in similar fashion one month later with the 'Bus Bomb' letter on November 9th 1969, stating 'I gave the cops som bussy work to do to keep them happy. I enjoy needling the blue pigs. Hey blue pig I was in the park -- you were useing fire trucks to mask the sound of your cruzeing prowl cars'.

It again emphasized that the Zodiac Killer was 'still here', almost reminding us of the fact he had never gone away. In many peoples eyes this aroused suspicions, that this letter was a poor imitation, crafted from the inspiration of previous correspondence. Nevertheless, this letter also signed off with the words 'yours truly' once again, in extremely similar fashion to the 1978 letter. See here. 
In the 1978 letter the author stated  'I am waiting for a good movie about me' and in the 1987 letter the author stated 'Cars make nice weapons. The pigs can catch me if they can find me out there. Just like in the movie The Car'.
The Zodiac Killer, if we take these two letters as genuine, appeared to be reminding the American public that he was definitely far from dead, as some press speculation had considered, due mainly to the Zodiac Killer's lack of correspondence subsequent to the 'Exorcist' letter in early 1974. But now he was back..... in fact he had never gone away.
Yours Truly-Jack the Ripper was a short story by Robert Bloch, published in Weird Tales in July 1943 was made for television on 11th April 1961, directed by Ray Milland and starring Boris Karloff, John Williams and Beverly Powers. See here.
In the story Sir Guy (John Williams) attempts to convince the police that Jack the Ripper is far from dead- in fact he is very much alive and still claiming victims- this time in New York. (see Albany Letter). In one line he says 'Now none of these Ripper murders received the notoriety of those in London, many went almost unnoticed, but they did occur' and went on to elaborate 'I've studied everything about them, especially the dates and the pattern made by those dates, I've studied their rhythm, the solar and lunar rhythm'. See here.
The police thought these new murders were a copycat, attempting to replicate the murders of Jack the Ripper, and poured scorn on the idea he was still around. Could the Zodiac Killer have read the book or viewed this television episode and deliberately signed off these later letters with the phrase 'yours truly' to again ridicule the police and authorities, who thought, that he was dead also.