Fred's point in saying that the police officer has no option to back away refers not to tactics, but to the fact that the sworn officer has the duty to pursue and apprehend a dangerous criminal one way or another within the limits of law and department policy.
The civilian, on the other hand, generally has an obligation to do whatever is safely possible (the safety of certain third persons usually enters into the determination) to avoid the use of deadly force and is not encumbered by a responsibility to chase down a suspect and make an arrest.
As you expect, I understand all this. I just don't think it therefore means that LEOs operate under AOJP, and non-LEOs operate (instead) under ADEE. Rather, that ADEE is an appropriate tactical mnemonic for private citizens, and AOJP is the proper legal justification mnemonic for private citizens.
ADEE and AJOP are not in opposition. And AOJP
absolutely applies to private citizens.
In fact, even where there is no Castle or Stand Your Ground law, tactical considerations are probably slightly more constraining than legal ones. Tactically, a citizen is "forced to" stand and fight any time his retreat is more dangeorous than fighting; legally, he may elect to stand and fight whenever he cannot retreat in safety--even if fighting is more dangerous than fleeing, legally he need not flee if fleeing is dangerous.
"Duty to retreat" in those situations were it exists does not mean one must retreat even where that retreat endangers you; you must legally retreat only if it is safe to do so. And that "retreat in safety" phrase includes the safety of those the defender has a duty to protect; if I pursue an attacker who has broken off his attack on me to head toward my wife (placing her under lethal threat), then I am pursuing legally.
Of course, if a defender is covered by a Castle law or SYL law, he may stand and fight even if he can retreat in complete safety. The effect Castle laws and SYL laws is to (in effect) remove the argument that the defender could have retreated in complete safety, which would then invalidate the SD claim.
Again, I don't think we are arguing, just clarifying.
police officer must remain engaged until his or her duty is done
The private citizen also must stay engaged until his duty is done. For him, however, the duty when under deadly attack is limited to protecting himself and his family with deadly force until the attack is over (that is, until AOJ no longer apply, or until he and they can retreat in safety).
I don't believe that AOJ was "developed" or traditionally "intended" to cover only sworn officers. Just the opposite, I believe it covers the elements of the legal use of deadly force by any citizen, and derives from (English) common law.