Who Murdered the Duke of Gloucester? Part 5

For someone who never appears in the play, the Duke of Gloucester and his murder comes up again and again.

Right before Bolingbroke is crowned, the subject is resumed. Bolingbroke asks Bagot to come forward and reveal who persuaded King Richard to have Gloucester put to death:

Now, Bagot, freely speak thy mind;
What thou dost know of noble Gloucester's death,
Who wrought it with the king, and who perform'd
The bloody office of his timeless end.
(IV.i.3-5)

Bagot comes forward and accuses the Duke of Aumerle, the son of the Duke of York, of being responsible for the deed:

My Lord Aumerle, I know your daring tongue
Scorns to unsay what once it hath deliver'd.
In that dead time when Gloucester's death was plotted,
I heard you say, 'Is not my arm of length,
That reacheth from the restful English court
As far as Calais, to mine uncle's head?'
(IV.i.813)

After Aumerle denies the charge, Lord Fitzwater comes forward and accuses Aumerle as well:

By that fair sun which shows me where thou stand'st,
I heard thee say, and vauntingly thou spakest it
That thou wert cause of noble Gloucester's death.
(IV.i.35-37)

After Henry Percy and another lord join in Bagot's accusation of Aumerle and the Duke of Surrey tries to refute it, Lord Fitzwater adds another detail to the plot against Gloucester:

As I intend to thrive in this new world,
Aumerle is guilty of my true appeal:
Besides, I heard the banish'd Norfolk say
That thou, Aumerle, didst send two of thy men
To execute the noble duke at Calais.
(IV.i.78)

Aumerle then accuses Norfolk of lying and asks Bolingbroke to recall Norfolk so that he may have the opportunity to refute him, but Carlisle informs them that Norfolk is dead. The bishop describes Norfolk as fighting for "Jesu Christ" and finally giving his "pure soul unto his captain, Christ" (IV.i.93, 99). This adds credibility to Norfolk's words, as does Norfolk's earlier denial:

...For Gloucester's death,
I slew him not; but to my own disgrace
Neglected my sworn duty in that case.
(I.i.132-134)

This most likely means that Norfolk's sin was to permit the two executioners sent by Aumerle to murder Gloucester rather than protect him in while he was in custody.

This part of the scene ends with the new king telling the accusers and the accused that he will set a date for their trial by battle.

Why does the subject of Gloucester's death come up again? Presumably to remind us of the wrongs of the king who is about to be dethroned.