Assuming white hats didn't know about this hit, or they would have stopped it. Only after did they realize someone on the flight is related to U1 and dossier. Thus the person hit was probably not someone who had flipped, but also a black hat being taken out by more senior black hats.
The dossier was always part of the insurance to protect U1 scheme. The person killed was like a source to steele, trying to protect himself as much as others.