When does an officer's discretion end, and where does an officer's duty begin?

Question

User6726's answer to this question seemed to imply that an officer's discretion was endless; that no matter what the situation, they could always decide not to intervene. That seems highly unlikely to me; surely if an on-duty, not undercover cop saw for example a stash of illegal weapons in the open trunk of a car, with the criminal sleeping inside it, they would be obligated to act?

My suspicion is this: there isn't really a point where they're no longer allowed to use discretion. More likely, I think they always possess discretion and duty at the same time; they have a duty to stop crime to the best of their power, and they have the discretion to decide whether they're capable of stopping the crime at that point with more benefit than loss. No matter the situation, they technically possess the right to deem the situation too something to not intervene; their duty lies in making that judgement earnestly.

Which is where the practical line between discretion and duty comes in: as said, I think they probably exist at the same time, but certain situations are of a nature that it becomes clear beyond a reasonable doubt that the officer did not exercise their discretion earnestly. In these cases, they would face reprecussions not because they used a discretion that they didn't have, but rather because they clearly violated their duty to use that discretion earnestly. In the kinds of situations where e.g. a criminal is aiming a gun at someone, a cop may decide to not intervene due to their tactical/psychological/whatever judgement of the situation/criminal telling them that intervention would be more likely to cause more harm, and thus I expect a lot of violent situations to fall on the discretion side of this line. So, then the questions arise:

1. Does such a line exist, and if so, what does (if anything) the law say about it?
2. How is this line evaluated in practice?

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I'm interested in the US jurisdiction. Someone mentioned that this depends extremely on the particulars of the situation. I'm more looking for an overview of the categories of situations that are usually treated as an "officer's discretion rules" versus the categories of situations where this isn't the case.

To aid in this, I'd like answers containing constructed scenarios (like my example of the criminal sleeping in his gun-loaded car) where discretion practically doesn't rule (practically doesn't rule in the sense I described above), and constructed scenarios where discretion definitely rules, and lastly, the constructed scenarios where it very much falls in a gray area that needs to be scrutinized due to a high contingency on the particular detials.

Of course, the constructed scenarios could be replaced with real-life cases.

Answer 1

There is an important distinction between moral duty and legal obligation. Even if an officer should arrest a person, given some moral standard, they are not legally obligated to do so. A test for legal obligation is whether an choice results in a negative legal outcome – is the officer sued or criminally penalized for acting or not acting? Unsurprisingly, the answer to the legal question is highly dependent on jurisdiction. I only consider US jurisdiction here (which incidently is not a single coherent jurisdiction, it is a phylum of jurisdictions), though some aspects of the answer extend to other countries.

The clearest cases are obligations to not act in a certain way – prohibitions. Police may not beat a suspect in order to obtain information. Period, end of story, no discretion. There is a putative bright line that police cannot cross, namely violating an individual's rights, and that constitutes a major exception to the doctrine of police immunity. If X is a clearly established right, police cannot violate that right and if they do, they can be sued or even prosecuted. Sometimes courts "discover" a particular right in a certain case, so the individual (plaintiff in a civil case) may be vindicated but the officer will not be subject to legal sanctions, since LEOs are not held to be appellate court justices who can divine the future discover of a legal right. 18 USC 242 statutorily describes certain circumstances where a choice is criminally proscribed, and 42 USC 1983 allows for civil suits. This pertains to things that an officer does, saying what an officer does not legally have the discretion to perform an act.

Now setting aside proscriptions where "you may not...", the doctrine of sovereign immunity prohibits civil or criminal actions against the government (including LEOs) unless a specific exception has been carved out. I recommend this (open access) journal issue on Discretion in Law Enforcement. There do exist statutory obligations to act imposed on LEOs, for example see this AG legal opinion from Florida, stating that

A law enforcement officer, including a police officer, has a legal duty to provide aid to ill, injured, and distressed persons who are not in police custody during an emergency whether the law enforcement officer is on-duty or acting in a law enforcement capacity off-duty.

A famous case regarding (non)liability for police inaction is Castle Rock v. Gonzales. In this case, police declined to enforce a Temporary restraining order (TRO) against plaintiff's estranged husband (who then murdered the children). The Supreme Court observes that

the Due Process Clause does not “requir[e] the State to protect the life, liberty, and property of its citizens against invasion by private actors”

and also noted the lack of express statutory obligation to enforce that law. In Everton v. Willard, the Florida Supreme Court addressed the question of whether

discretionary police power authority to make or not make an arrest and whether a decision not to take an individual into custody constitutes a basic judgmental or decision-making function that is immune from tort liability

and they do

hold that the decision of whether to enforce the law by making an arrest is a basic judgmental or discretionary governmental function that is immune from suit, regardless of whether the decision is made by the officer on the street, by his sergeant, lieutenant or captain, or by the sheriff or chief of police

There have been disagreements on sovereign immunity, for example Huhn v. Dixie Insurance Co., 453 So. 2d 70, which held that

when an individual suffers a direct, personal injury proximately caused by the negligence of a municipal employee while acting within the scope of his employment, the injured individual is entitled to redress for the wrong done

(the relevant action was not arresting a person for DUI).

As employees of the government, LEOs are subject to the over-arching rules of their employer. They may be ordered by their superiors to refrain from arresting a law-breaker during a riot, on the grounds that doing so will exacerbate a tense situation. The police department might be sued for such a decision, but it is unlikely that the government will be held liable for an essentially political decision. Likewise, enforcement of "no public camping" laws is highly variable, and the courts will most likely not sanction a city for not arresting homeless people who are camping on public property in violation of the law.