Also, when you frop out of SC, your ships thrusters are automatically set and tour ship is moving.
He wasn't just moving, he was boosting away, as he himself stated in his original post. Boosting is clearly an attempt to escape, and I even waited for him to stop for a while, which didn't happen. If he is trying to figure out the comms system or just ignoring me, I cannot tell, so attacking seemed to be the best bet. Attacking without the intention to kill you should note... I targeted his engines in order to stop him from fleeing. Not much harm done aside from a few credits for repairs. Since the introduction of rebootable modules, disabling one's engines is no longer a death sentence.
To be honest I'm currently thinking of opening fire right away next time, disable the engines, and then communicate my demands. Every second counts, if you don't want to watch your prey jump away.
Tou can tell when someone activates their FSD when you have them targetted easy enough.
Try it out yourself one day, so you get an idea of what you are talking about. If you wait for the FSD to charge, you can as well not interdict at all in the fist place, because it is too late.