Complex sentence: Members of the Protestant Apprentice Boys of Derry were angered by this, considering it a deliberate insult to the monarchy; in a sectarian riot that evening three Apprentice Boys were shot dead by the Londonderry Borough Police.
Split into simpler sentences: Members of the Protestant Apprentice Boys of Derry were angered by this as they felt it was a deliberate insult towards the Monarchy. This led to a sectarian riot between the two factions that evening where three Apprentice Boys were shot dead by the Londonderry Borough Police.