New Delhi, Sept. 13 -- The words 'Bella Ciao' were found engraved on the casing of the bullet that killed conservative commentator and Trump ally Charlie Kirk last Wednesday, shocking both investigators and the public.

The phrase, a reference to a famous Italian protest song, has since triggered a wave of online debate, confusion, and outrage.

But what exactly is 'Bella Ciao'? And how did it end up as a symbol, however twisted, at the centre of a political assassination?

"Bella Ciao" dates back to at least the early 20th century and is best known as an Italian folk anthem adopted by the partisans-anti-fascist fighters who resisted Benito Mussolini's regime and Nazi occupation during World War II.

Though the exact origins are debated, ...