Creon accuses Haemon of being a "soul of corruption, rotten through...."( 837) Haemon rebuts that actually his "concern is all for [Creon]." (830) He states that he "sees [his] father offending justice." (833)
What does Haemon mean by this?
Creon does not actually have the power to sentence the daughter of King Oedipus to death and is, therefore, circumventing justice by doing so.
Creon should not ignore the gods' edict about killing royalty, who should not be stoned in the street. Instead, he should come up with another punishment.
By not burying Polynices, Creon trampled on the laws of the gods. In executing Antigone, who was only obeying the gods' laws, he is further offending justice.
Creon needs at least one witness of royal blood to the crime to be able to sentence Antigone to death; since he doesn't have such a witness, he cannot execute her.
Because Ismene knew about Antigone's plan to bury Polynices but said nothing, she too should be punished, if Creon is really just.