Socrates was brought to trial as a result of his teachings and his outspokenness.  He defended himself courageously saying that  he had to speak the truth as this is what is essential in the correct conduct of one's life  He told the jurors that correct action involves thought, and therefore virtue can be taught.  To him knowledge was correct action.  

The jury found him guilty of several charges, such as corruption of the youth etc, and sentenced him to death by drinking poison.  He drank the poison calmly  and heroically overlooked by many of his followers, never reneging upon his beliefs.

In his philosophy Socrates rejected the relativism of the Sophists and the belief that it is impossible to arrive at what is right and wrong.  He agreed with the Sophists that distinctions do exist in customs between any two cities.  He argued that the animal world cannot be used in comparison to humans.  The essential problem with mankind in his eyes was the ignorance and lack of insight into the nature of good and evil.