Texas was the first thing to come to my mind : http://nation.time.com/2013/06/13/when-you-can-kill-in-texas...
The laws do seem to allow less after the fact, with good reason. My point was that we clearly allow for people to value money over lives.
When is a robbery over? The stuff never stops being yours, and they never stop running away with it.
A lot of things come into play here, but I'm pretty sure you could still post a reward, 'dead or alive'. I think it's legal to try to catch the robber yourself indefinitely, and defend yourself if threatened in the process.
Our wild west laws are only slightly less savage than what was alleged in this case.