From what I know
The Non-Aggression Principle,

Is not designed.
It is not a tactic.
It is not an attempt at regulating crime through intimidation by retaliation
It is not a system.
It is not about what happens afterward (retaliation, penalty's, therapy or whatever)
It is not a law or rule or statute.
You can't enforce it.
You can't make it into a written law.
Or a contract that everybody signs.
You can't make it a right or a command.
You can't enforce it.

It's a principle.
It's about self-defence.
It's not initially about a solution to stop or prevent crime or about punishment or therapy or whatever come's afterward.

This is what I understand about it.
For the difference between a principle and a law, you could read.
http://achterdesamenleving.nl/wp-content/uploads/2014/10/The_End_Of_All_Evil_by_Jeremy_Locke.pdf