The jurors volunteered. Their names were chosen by lot for random service over a one year period. They were called judges as there was no presiding judge. Like today, jurors were paid, but the expectation was that one should really do jury duty as a service to the community (thus, like today, the compensation was modest). Nevertheless, many jury volunteers were old men who lacked other means of livelihood. Each took an oath to make judgment according to the laws of Athens.
Given a jury of five hundred, the fact that thirty swing votes would have
resulted in Socrates' acquittal made the vote
very close. Now, because Socrates had been convicted
of a crime for which the law required no set penalty, a second round of voting
was necessary to determine punishment. This procedure called for the prosecution
to propose a penalty and the convicted person to propose a counter-penalty.
Then, the jurors had to decide between these proposals and were not empowered
to choose a third alternative!