MDPD units such as the one who conducted this investigation are usually very thorough and they're supposed to have everybody in the vicinity in question under direct supervision and in some cases such as this one, even restrained. They weren't watching their 6 for whatever reason. Then this nut bag got the drop on them.
My first comment, I apply that again. They know better than that. There was probably an informant involved that isn't mentioned in the story. It happens here a lot, getting too comfortable.
Sáncte Míchael Archángele, defénde nos in proélio, cóntra nequítiam et insídias diáboli ésto præsídium. Ímperet ílli Déus, súpplices deprecámur: tuque, prínceps milítiæ cæléstis, Sátanam aliósque spíritus malígnos, qui ad perditiónem animárum pervagántur in múndo, divína virtúte, in inférnum detrúde. Ámen