Ricci never got caught either--for this crime.
We were talking about putting airplane glue on fingertips, not the Brinks robbery. Ricci spent so much time in jail, and what do they do in jail? Compare stories--during which exercise they learn their trade even better.
Zodiac was surely a person of high intelligence; it doesn't take genius-level intelligence to think of trying something like airplane glue on the fingertips.
People always assume that "if Ricci did it, he must be a criminal mastermind," because "there was no evidence." Fact is, there WAS evidence. The criminal case was in its infancy. It had not yet shaped up; figuring out whether it ever would have shaped up is like trying to figure out what sort of person an aborted baby might have turned out to be.
One huge factor that led to Zodiac never being caught is that there were competing jurisdictions. Sometimes one jurisdiction would even keep evidence hidden from another jurisdiction. Read one of Graysmith's books, and you'll see this discussed.
Chief Dinse on more than on occasion stated that he would charge Ricci in a second if he had any evidence, but that he did not have any, so he didn't charge Ricci. these are Dinse's words, not mine