Not the earliest but best remembered from childhood was the footage of a PHRASECENSOREDPOSTERSHOULDKNOWBETTER. mob assaulting two British army officers, who were handed over to and killed by the IRA.

Remember earlier news events like the Brighton hotel bombing, but watching the assault as a kid, in disbelief that this could be happening in the UK.

http://www.bbc.co.uk/history/events/army_corporals_killed_at_ira_funeral