The tentative plan as it has been posted a few times is that you'll need to beat someone down to 1hp prior to arresting, so that addresses this exact question. :)Edited By: Syn on Year 16 Day 90 15:06
Part of the purpose of this is so you need to deliberately make the choice to make a kill shot versus capturing your enemy; Zhao had previously expressed that he wants character kills to be deliberate choices made by other players so your npcs can't accidentally kill someone you wanted to capture. He wanted character death to be valued enough that it wouldn't be something that happens due to accidental or random factors. The recoding of black holes to work like suns and be routed around automatically was a step in this direction for the same reason.
Again, this is all subject to change depending on implementation needs but that's been the plan so far.
The current implementation has already been correctly described by Ulrike and Tomas.