Yes, my thought is maybe he chambered it on the bridge and tried to fire it at the CS, but the firing pin was bad, so he chambered another round, which ejected the unspent round. When he fired again, it didn't work either due to the firing pin issue. But he didn't chamber again, because he went to his knife, thus only one unspent round ejected and the other he kept as a souvenir in his keepsake box. It's just a random idea. I don't know how much I believe it, but it would be great if the firing pin left identifiable marks on both rounds. JMO. We maybe don't know about the primer marks.