How to crack Zodiac

The Zodiac left a maze of riddles and ciphers for not only police to solve but people from all over and I think he hinted on how to solve his famous 340 cipher, which was solved eventually and is similar to how a knight can move in chess when he referred to this as a game, which points to chess?

The only other thing was that he was using a Homophonic cipher which I did find a backdoor recently, but it doesn't apply to this because the cipher is still different from all others.