If it was on an accessible roof, where you can get on to it, I would be defending you, as you would have no indications that it was an admin sit, unless you see people jailed, frozen etc. On the other hand, it was not on an accessible roof. Therefore, the only way to get up is with special suits, teleporting/noclip or prop climb. To add to this, if there was 2 or 3 people, it would be more suggestive of a sit. From the perspective of Ashur, you were shooting people in a sit, which was true. From your perspective, it seems you are saying you didn't know it was a sit at the time. At the end of the day, you did kill someone in a sit, so it was against rules.
Well, that's my take on it.