Is there some sort of clip available for the situation?
From what is stated, it seems that his character was not under fearRP. With that being said radioing a message does not constitute a valid kill under the 'killing rules' of the ImperialRP rulebook. Even if he was under fearRP, the NSB, just like anyone else should be held to the consistent standard of what is laid out, for each shooting they must have either a reasonable "Active Threat" or they are allowed to kill someone under only after multiple and repeated warnings to the person that they have under fearRP. (General Rules §2 and FearRP Rules §3)
Additionally, in fearRP rule §4 clearly states
You must have a valid reason to place someone under FearRP (I.E. Reason to forcibly detain, question, kidnap, or mug). Placing someone under FearRP without reason or just to bait a PK is not permitted and may result in a ban or character removal.
The NSB were going around the entire military base asking for IDs, and put every military member they came in contact with under FearRP, directly violating FearRP rules and targeting those in specific factions for no real RP reason. Additionally §6 states
Continually putting yourself into FearRP scenarios in order to PK people, or 'PK hunting' / being 'PK hungry' is not permitted (Mass Mugging, baiting, shootouts on alt characters, etc.). If staff feel as if you are performing these acts intentionally with no regard for actual roleplay, they may deny your PK requests and/or issue punishments.
The NSB, by going around an entire military base and putting many people under fearRP, who could not have been their one specific target, as they knew the person they were looking for was a Heer Officer, violated §6 by PKing someone that they had no RP reason to be putting under fearRP by doing what is essentially mass mugging/baiting these situations by putting large amounts of people under fearRP with no regard to actual roleplay. For these three main reasons, which should be reasonably known by any Staff member and whomever was leading the NSB's roleplay, his PK should be reversed and the person in charge of the NSB operation should be punished as his faction did what was essentially Mass Mugging and PK hunting with no regard to actual roleplay.