The rifle is bolt action. The spent casing was still chambered.
I do find it interesting that DOJ lawyers have been seeking the death penalty for Mangione, and linchpin of their case is that he inspired other shooters – something that until recently was openly laughable.
Adding that the story of the supposed writing on the bullets is based on a memo that circulated at the FBI and it’s unknown if that memo was based on accurate information or just the figment of someone’s imagination to create a narrative that people will now just accept as fact.