http://www.thehighroad.org/archive/index.php/t-474161.html#.UVK4XfP4dpY.gmail
Here’s Washington State Law; note that it pertains to citizens, not law enforcement, who are covered in another point of the same chapter:
RCW 9A.16.020
Use of force — When lawful.
The use, attempt, or offer to use force upon or toward the person of another is not unlawful in the following case(s):
(2) Whenever necessarily used by a person arresting one who has committed a felony and delivering him or her to a public officer competent to receive him or her into custody;
So in theory, any citizen can use whatever force is necessary to arrest (i.e. stop) a felon. However, the Tennessee v. Garner case must be taken into account for citizens as well as for LE; and the gist of that is that you need to assess and balance the risk of using force against this person vs. the risk of allowing them to escape. Are they going to harm someone? Have they already done so? How dangerous are they? That’s all Garner requires us to articulate.
There are certainly cases in which I would shoot a fleeing felon in the back, LE or not; and that decision would arise out of a conviction that they represent a totally unacceptable danger if allowed to escape. Both the Law and Garner envision and allow for this kind of possibility.
Justified use of force (to arrest someone for theft) isn’t necessarily self-defense, though. I think there has to be the possibility of a threat to life to justify the use of deadly force.
Of course, armed criminals who have committed a crime (especially already shot someone) and are fleeing might still pose a threat. They could turn and shoot at any moment, or they may be fleeing to find cover and then to shoot again. I don’t think you should have to wait until they turn and take aim at you. I can see justifying shooting them as self-defense under those conditions.