In the two versions of WH40K Roleplay I have access to (Deathwatch and Only War) the Overwatch action is presented with largely identical text, as follows:
The active character guards a specific area or target, poised to shoot at an opportune moment. When Overwatch is declared, the active character establishes a kill zone, which is any general area, such as a corridor or treeline, that encompasses a 45 degree arc in the direction that active character is facing.
The active character then specifies [an attack type], along with the conditions under which he will perform the chosen attack. At any time the specified conditions are met before the start of the character’s next Turn, he can perform that attack. If this attack occurs at the same time as another character’s Action, [...]
Additionally, targets caught in the kill zone must make a [...] Pinning Test or become Pinned (see Pinning on page 248). If a character on Overwatch performs any Actions or Reaction, such as Dodge, his Overwatch immediately ends. Note this does not include Free Actions, such as speech.
It's not clear if resolving the attack (as part of the Overwatch action) is counted as "performing an Action", which would end the Overwatch. The sentence "At any time the specified conditions are met before the start of the character’s next Turn, he can perform that attack" can be interpreted two ways:
Each time the trigger condition occurs, the character may choose to resolve the attack (which ends the Overwatch) or not resolve the attack (saving the Overwatch for a potentially greater threat)
The attack may be resolved each time the trigger condition occurs (but the character may choose to hold fire, e.g. if the triggering entity is non-hostile)
I've searched forums and found a number of debates on the topic but no official ruling. Is there any official clarification of exactly how this works? I will accept an official clarification given for any Warhammer 40,000 Roleplay game line, since as far as I can tell the Overwatch rules are very similar for all of them.