What did Casy's death symbolize in The Grapes of Wrath?

Casy's death represents several elements in the
narrative.  The first is that it shows the lengths that the "owners and their minions"
will go to silence the truth from being spoken.  Casy's death is not an accident.  It is
a reflection of how violence is used to suppress dissent in an industrialist
configuration where the struggle and desire for wealth outstrips the compassion and care
for human beings.  At the same time, his death is a representation of the result of the
protection of these economic interests.  Casy's death also represents a critical moment
for Tom.  He is linked to another human being, a condition that moves from him isolation
to collectivization and solidarity,  Tom kills in defense of another human being. This
shows that Casy's death has accomplished a change in Tom, something that shows his own
care for human beings.  This is a condition that was not in his character at the start
of the novel, one where he simply wished to be "left alone."  Now, he is convinced that
his calling and his purpose is to be linked to other people and a larger community,
something that is brought out in Casy's death.