In Macbeth and Julius Caesar, murder is presented as the act that destroys political stability and plunges society into chaos. After Macbeth murders King Duncan, Scotland is robbed of its rightful king, Duncan's rightful heir Malcolm must flee for his life, and Macbeth becomes an illegitimate, detested king. The country is thrown into political chaos, civil peace is destroyed, and suffering ensues. Similarly, in Julius Caesar political stability is destroyed by Caesar's assassination and the power vacuum produces a violent power struggle. The forces of Antony and Octavius go to war against those of Brutus and Cassius. After Antony's speech at Caesar's funeral, mobs surge through the streets, burning and killing. Rome is plunged into chaos. In both of these plays, the murder of the ruler and head of government brings enormous and disastrous consequences.
Murder is more than a political act, however, in each play. Caesar's murder, however Brutus might try to justify it, is presented in its horror. An unarmed Caesar is surprised and set upon by a group of assassins who stab him to death, one striking after the other. King Duncan, a wise and just monarch, is also set upon when he cannot defend himself. He is sleeping when Macbeth hacks him to death and leaves the scene of the murder covered in the King's blood. Furthermore, in Macbeth one foul murder follows another. Murder becomes the means of a tyrannical monster (Macbeth) to remain in power. Without pity or hesitation, he orders the additional murders of men, women, and children, all of whom are surprised and defenseless, attacked by groups of killers.
In both of these plays, nothing good comes of murder. Murder results in warfare and further destruction. Brutus and Cassius kill themselves when faced with defeat by Antony and Octavius; Lady Macbeth commits suicide after descending into madness; Macbeth is beheaded by Macduff in battle. When Macbeth, Cassius, and Brutus chose to shed blood, their acts of murder opened the floodgates of violence. As Macbeth himself said, "[B]lood will have blood."
Murder is a major theme in many of Shakespeare's tragedies. It is the murder of Hamlet's father that initiates the plot in Hamlet with the appearance of the ghost asking for a revenge. Among many deaths that follow there are further murders: murders of Polonius, Claudius, Laertes & Hamlet himself. The theme of murder & bloodshed, an element of Senecan Revenge Tragedy was adopted and wonderfully remade by Shakespeare as the main-stay of his dramatic plot.
We also have a number of murders in Macbeth. The murder of King Duncan by Macbeth sets the action rolling. Then follows a series of murders--of Banquo, of Macduff's wife and children, secret murders let loose by the usurper king, Macbeth, and the killing of Macbeth by Macduff.
To come back to the theme of murder in Hamlet, we may take note of the following:
a) The murder of Hamlet's father shows how relationships are vitiated by unholy passions of the mind. Hamlet's uncle, Claudius, kills his brother in connivance with Hamlet's mother, Gertrude.
b) Polonius is killed by Macbeth because Polonius serves as an agent & confidante of Claudius who represents evil.
c) The murders are related to Shakespeare's treatment of the problematic of evil.