Complex sentence: Many consider that the spark for the events in Ireland was the murder of the unpopular Earl of Leitrim in April 1878, where his three assailants went unpunished from a lack of evidence as no witness wanted to testify against them.
Split into simpler sentences: Many consider that the spark that set off the events in Ireland was the murder of the unpopular Earl of Leitrim in April 1878. The three assailants went unpunished due to a lack of evidence as no witness wanted to testify against them.