Why Were Live Rounds on the Set of Alec Baldwin's 'Rust'?

A probe into the fatal shooting of cinematographer Halyna Hutchins on the set of Alec Baldwin’s movie “Rust” in New Mexico has found ammunition at the scene that investigators suspect to be “live rounds,” authorities have announced. Business Insider reporter Claire Atkinson explains why live rounds may be found on a movie set, and breaks down what questions remain to be answered about the deadly incident.