He had no association with the thirty whatsoever. Two were former students. That's it. And not only did he not participate (nor would he have been invited to participate in any case) but he actively opposed them while telling them that he did not fear death - an assertion they undoubtedly would have put to the test, sooner or later, had their government lasted longer than 8 months.

And as for his trial the indictment against him read, "This indictment and affidavit is sworn by Meletus, the son of Meletus of Pitthos, against Socrates, the son of Sophroniscus of Alopece: Socrates is guilty of refusing to recognize the gods recognized by the state, and of introducing new divinities. He is also guilty of corrupting the youth. The penalty demanded is death." Socrates intentionally provoked the 500 jurors with statements such as, "Men of Athens, I honor and love you but I shall obey God rather than you, and while I have life and strength I shall never cease from the practice and teaching of philosophy." The use of "God" and not "Gods" was not an accident. When Socrates was asked to propose his own punishment (in lieu of death) he proposed he be rewarded.

He obviously was not surprised when he was found guilty. The jurors were 500 random Athenian men, hardly his compatriots. His parting words speak of his intention, "The hour of departure has arrived, and we go our ways - I to die, and you to live. Which to the better fate is known only to God." He knew he had lived a great life and one that would extend well beyond himself. His martyrdom here was the grand finale to emphasize the correctness of the unpopular things (within Athens) that he had been saying all along. He warned that Democracy can become an unreliable and capricious system. Democracy responded by murdering him. You're undoubtedly correct that some of the majority that decided he should be murdered were driven by a misguided lust for revenge. That is a key validation of everything he ever said, and he knew it would be.