Are law enforcement officers obliged to apprehend a subject committing a crime at the earliest possible opportunity? Inspired in part by this question: if a person is committing crimes of increasing severity, are law enforcement personnel obliged to apprehend them at the earliest opportunity? Specifically, are they obliged to prevent a crime at the stage where it is a conspiracy, or attempt, to commit it? If so, in what circumstances? For the sake of simplicity, let's consider only US cases.
The circuits all over the place on this one but in short, no, police are not obliged to apprehend a suspect at the earliest opportunity. It is within the discretion of the police to decide whether delaying the arrest of the suspect will help ensnare co-conspirators, as exemplified by this case, will give the police greater understanding of the nature of the criminal enterprise, or merely will allow the suspect enough "rope to hang himself." U.S. V. Garcia 79 F.3d 74 (7th Cir. 1996) See also Hoffa v. United States 385 U.S. 293 (1966) A suspect has no constitutional right to be arrested when the police have probable cause. The police are not required to guess, at their peril, the precise moment at which they have probable cause to arrest a suspect, risking a violation of the Fourth Amendment if they act too soon, and a violation of the Sixth Amendment if they wait too long. Law enforcement officers are under no constitutional duty to call a halt to a criminal investigation the moment they have the minimum evidence to establish probable cause, a quantum of evidence which may fall far short of the amount necessary to support a criminal conviction.
In Connecticut, this is covered by the firefighter's rule. Police and fire personnel entering a property as part of their official duties are considered licensees, which limits the duties of the landowner. The rules are as follows: You can't intentionally hurt or lay a trap for the licensee. If you know or should know the licensee is there, you need to exercise due care with them. You don't have to worry about obvious hazards (but keep in mind that it's harder to see stuff at night). If you're doing something dangerous, you need to watch out for them. If you know about a hidden hazard, you must warn them. I'm not sure how in-depth you need to go with the warnings; various things I find suggest the duty to warn might only be there when you know or should know the licensee is present, but signs are a good idea regardless. On the other hand, if you do need to warn them, you might need to mention the specific locations of the pits you actually know about. However, there's no duty at all to proactively look for possible hazards. This rule originated as a rule for professional firefighters responding to a negligently-started fire: the idea is that professional firefighters sign up to do a dangerous job, and letting them sue for hazards inherent in their job (they aren't called without a fire) is a bad idea. Also, since they cannot be denied entry, go in places not open to the public, and can arrive at any hour, needing to keep the property safe for them is an unreasonable burden. Of course, there's an exception if a law is passed to protect their safety, because statutes override common law. The rule has since been extended in some states to police, and to situations besides the very problem they were called for. Other states have abolished it. In any event, this is for civil liability only: this is when cops can sue for injuries caused to them.
In the United States, there is no potential liability for the municipality or the police department. There is no legally enforceable duty of police to act to prevent either violations of the law, or apprehend criminals, or to prevent suicide of people who are not in police custody. Other countries have different laws on this subject.
There is a good amount of case law addressing this question going back two centuries. Legally, as soon as you are subject to "excessive force," you are allowed to defend yourself as you would against any assault, even if that force is being used in the course of an otherwise lawful arrest. Furthermore, in some states you are still allowed to resist unlawful arrest. Unfortunately, the matter is no longer as clear as it used to be. (There is a lot of material on this subject; just search for resisting unlawful arrest.) For example, police reflexively invoke a virtual safe harbor by shouting, "Stop resisting!" while battering arrest subjects. Video evidence has uncovered a plethora of examples in which this was done to subjects who were not only not resisting, but even later determined to have been incapable of resisting. If you intend to defend yourself against police, even when justified by law, you need to realize that the system is stacked against you. Police carry the means of escalating to lethal force. So, for example, if you are being beaten but you are potentially able to physically overpower and restrain an officer, you will likely then be met with baton blows or tasers. Since a baton is a deadly weapon, you would be (in theory) justified in shooting an officer attacking you with one. But as soon as any officer shouts "gun!" you will be shot, and most likely killed. Police seem to be given the benefit of the doubt by prosecutors and grand juries when they claim, "I feared for my life." You (even if you survive) will likely have any such claim subject to a full criminal trial. So even though you can legally defend yourself against excessive police force, these days you will almost certainly be unable to in practice.
If the conditions at s.17 and s.24 PACE 1984, and PACE Code G are satisfied for the offence of rape then there is no requirement for a warrant. Once the suspect is in police custody he may be further arrested for suspected harrassment if any of the necessity criteria are met - this will depend on the particular circumstances of the case. An either way offence is, for these purposes, regarded as an indictable offence. A constable does not need to physically see an offence being committed, but he must have (a) reasonable grounds to suspect an offence has been committed (b) reasonable grounds to believe an arrest is necessary (c) the requesit belief to satisfy s.17 PACE 1984. All this will come from conducting a proportionate investigation in to the allegations.
In general in the US, anyone may photograph anyone else if they are all in a public place, although in some states such a photo may not be used commercially without permission, which must often be paid for and may be refused. It is unusual for police to photograph people on the street, but they might want to document who was present at a particular place and time. They can do so, but I am not at all sure that they can prevent a person from covering his or her face, or turning his or her back, or charge a person who does so with obstruction. I don't think so. Under some circumstances in the US police may ask a person for identification, and may charge a person who refuses to provide it. This varied from one state to another, and usually depends on the specific circumstances. (If a person is driving an automobile, police may demand to see a driver's license, for example.) Unless a police officer puts a person under arrest, the officer has no general right to control that person's actions, beyond instructing the person not to interfere with ongoing police work. I do not think an obstruction charge would hold up for covering one's face or turning away in the absence of an arrest.
The General Rule In practice, the only time when self-defense against a police officer is legal is when you do not know and have no reasonable way that you could have known that the person attacking you is a police officer. (And arguably, a police officer acting in an official capacity in furtherance of his or her duties, rather than in a personal capacity as an individual.) For example, if the police do a no knock raid in the dark of night, and don't announce themselves, and you shoot police officers reasonably believing them to be home invasion burglars, you would not have criminal or civil liability for doing so. A similar valid self-defense claim might arise when someone has an objectively reasonable reason to think that someone claiming to be a police officer is really just a criminal impersonating a police officer, even if that belief is, in fact, mistaken. In almost all other circumstances, you need to submit to the officers, and you are pretty much required by law to bear the risk that excessive force by the officer will harm you. If you don't, you will probably be guilty of the crime of resisting arrest and will not be entitled to a self-defense defense. The fact that you are not actually guilty of a crime is irrelevant. This is often the case and police officers are not omniscient. If the officer lacked probable cause for an arrest (which there is often no way that the person being arrested or attacked can know at the time), the remedy is a civil rights suit after the fact, not self-defense. In theory, there might be other isolated circumstances where self-defense against a police officer is legal, but they involve fact patterns so quirky that they would almost never happen in real life, or would almost never be possible to prove in a manner that the courts would believe. Officer Liability For Harming Someone Legitimately Acting In Self Defense Whether the officers had civil liability to you if you were harmed by the officers while exercising your right to self-defense would depend upon their state of mind, even if you were rightfully using self-defense. For example, a U.S. Supreme Court case decided in January of 2017 (White v. Pauly) involved this fact pattern. In White v. Pauly an officer arrived late on the scene and had no reason to believe that the officers who arrived there before him and were being shot at by citizens in a house that they were approaching, lacked probable cause, or had not announced themselves. The court held that as a result, he had no civil liability to a citizen he shot, even if the person who the late arriving officer shot while that citizen was shooting back at the police officers on the scene was actually engaging in good faith self-defense. The citizen's self-defense in the case had a valid defense to criminal or civil liability for firing on the officers, because the citizen shooting back didn't actually know that the people approaching his house were police officers. But, because the late arriving officer reasonably believed under the circumstances that the citizen had no right to engage in self-defense, because he thought that the early arriving officers had probable cause and had announced themselves, the late arriving officer had no civil liability to the citizens he shot.
The advantages are: police officers, like all enforcement officers, have discretion on how they treat what they perceive to be transgressions of the law they enforce. If you are cooperative and helpful they may exercise that discretion to your benefit, if you are obstructive and difficult they may exercise it to your detriment: this may be the difference between a warning, a ticket and an arrest. one of the things that judges are allowed to take into consideration when sentencing is remorse. While the linked podcast indicates that this is not an easy thing to objectively define, it includes accepting that what you did was wrong and mitigating the harm that was done which would include cooperating with law enforcement. The disadvantages are: you may reveal information that is not known to the officer. This may or may not be admissible evidence but, notwithstanding, it may serve as a basis for further investigations which can discover things you would rather the police officer did not discover. For example Officer: "Do you know why I stopped you?" You: "I assume because of the dead body I have in the boot."