Not sure. There's a lot of people who've served in the US military. Factor in that those are the ones who probably have a better understanding of how to create IEDs, it's probably not that unlikely.Two attacks confirmed by people serving in the US military, seems a real odd outcome
A better question would be to ask why, after years of apparently exemplary service, a person would go full depart? A high probability guess would be one involving sky fairies.