Players with -5.0 or worse are considered outlaws.

With negative standing, where can pilots travel?

Players with better than -2.0 can enter any system
Players with -2.0 or worse cannot enter 1.0 systems
Players with -2.5 or worse cannot enter 0.9 systems
Players with -3.0 or worse cannot enter 0.8 systems
Players with -3.5 or worse cannot enter 0.7 systems
Players with -4.0 or worse cannot enter 0.6 systems
Players with -4.5 or worse cannot enter 0.5 systems

So when is it legal to kill someone?

In 1.0 - 0.5 systems, Concord will arrive on the scene and you lose security status
In 0.4 - 0.1 systems, Concord won't come, but you still lose security status
In 0.0 systems or below, nothing happens

CONCORD Response Times

0.5: Roughly 19 seconds
0.6: Roughly 14 seconds
0.7 : Roughly 10 seconds
0.8 : Roughly 7 seconds
0.9 and 1.0: Roughly 6 seconds