Does someone in the U.S. illegally have the same rights in court as a U.S. citizen? So right now in my home state of Iowa, an undocumented immigrant is on trial for murder charges. Apparently he wasn't read his rights when he was being investigated. Whether that is true or not, does he have those same rights as a U.S. citizen?
Everyone physically present in the US is protected by the US Federal constitution. (In some cases persons not physically in the US also have protection from the US constitution. When that applies is too complex for this answer.) Most of the rights protected by that constitution are available to anyone present, whether citizen, lawful immigrant, lawful visitor, or a person in the US without lawful authority. A few rights, such as the right to vote and to run for public office, are limited to citizens. If a person was arrested but not informed of his or her Miranda rights, then statements made to the arresting officers (or later interrogating officers) would not be admissible in court, unless an exception to the Miranda rules applies, which is unlikely. I can't say if this happened in the particular case mentioned in the question. In general, in the area of criminal procedure, there is no difference between citizens and others subject to US jurisdiction (accredited foreign diplomats normally have immunity). A few crimes can only be committed by citizens (or others owing allegiance to the US) such as treason. A few crimes, such as unlawful entry to the US, can't be committed by citizens, as citizens automatically have a right to enter. But criminal procedure and constitutional rights affecting criminal procedure, are the same for all in the US, citizen or not. (Oh, there are special laws for minors, but that isn't a matter of citizenship.)
I'm no expert, but I had assumed this clause was present in case of the following situation. Joe is arrested for a robbery of a London bank. Joe says nothing under questioning. At trial, Joe's defense is that at the time of the robbery, he was in Sheffield drinking beer with his brother. On the basis of common sense, a jury could think: "Surely if Joe were really innocent, he would have told the police of his alibi at the time he was questioned, and saved himself a lot of trouble. Since he didn't do that, maybe a more likely explanation is that he wasn't actually in Sheffield, but that sometime between arrest and trial, he came up with the idea of faking an alibi in Sheffield, and convinced people to testify falsely to that effect. Yes, that does seem more plausible. So we are not going to give much credence to Joe's supposed alibi." So it really would be the case that not mentioning the alibi during questioning would harm Joe's defense at trial. The warning, then, is intended to keep Joe from doing this inadvertently. If Joe's alibi is genuine, but out of a misguided desire to exercise his right to remain silent, he doesn't mention it during questioning, he may accidentally increase his chances of being wrongly convicted. Everybody has an interest in avoiding this.
If you falsely claim to be a US citizen in order to obtain work, vote in a US election, or receive public benefits in the United States, you can be deported, lose a green card, or be banned from ever obtaining a green card or US Visa. See https://dyanwilliamslaw.com/2015/02/why-lying-about-being-a-u-s-citizen-can-stop-you-from-becoming-a-permanent-resident-and-what-you-can-do-to-overcome-this-obstacle/ and https://www.nolo.com/legal-encyclopedia/how-falsely-claiming-us-citizen-can-deportable.html for more detail. This very much includes checking an incorrect box on an I-9 form when obtaining a job, although that is not usually considered a "benefit". In fact incorrect I-9 statements are a common source of such bans. However, if a person lies in response to a merely curious question, when no government or private benefit, and no job eligibility is involved, the ban should not, as far as I can see, come into effect, nor should that be grounds for deportation, or indeed any criminal or immigration action. If a person falsely claims to be a US Citizen merely to obtain social status or personal importance or reputation, that would seem not to be a crime under the doctrine of U.S. v. Alvarez, nor should it lead directly to any immigration consequences, althoguh I suppose it might draw attention to someone who is deportable on other grounds.
When a country makes criminal laws, these laws usually apply to anyone present in the country, and acting in the country. But the country is free to declare that some law might apply to its own citizens in a foreign country, or even foreign citizens in a foreign country. Assuming the laws about using marijuana say nothing about the country, that most likely means it only applies to using marjuana in the country itself. But if the US government decided that taking marijuana in Canada is illegal for US citizens, then nobody can stop them. In this case, Canada would not extradite you (unless Canadian law says that it is criminal for Canadians to use marijuana in another country), and Canadian police would likely not collect evidence. So even if illegal, it would be hard to convict you. PS. The "polygamy" case would be interesting, I think you would have to read the exact wording of the laws in every country. Some countries will say that you can't get married twice, and the attempt to get married a second time while already married is bigamy. In that kind of country you wouldn't have committed a crime within that country. Also, you would only be married to the first wife.
You are deeply confused, probably by the blogs of a conspiracy theorist (perhaps discussing the Sovereign Citizen Movement mentioned in the comments), whom it would be helpful for you to reference. In fact, people with and without lawyers claim common law rights in the ordinary courts of the UK every day, in the lion's share of civil lawsuits. For example: There is a common law right to sue for damages when someone breaches a contract by not paying a bill that they owe. A defendant, meanwhile, has a common law right to defend against such a suit on grounds, for example, that the debt has been paid or that the debt is not owed because there was no agreement to pay in the first place. The substantive right of an owner of real property to evict a tenant who breaches a lease arises at common law, even though statutes spell out the process for enforcing that right. Furthermore, the way that ownership of real property is established (i.e. through a chain of title involving purchases by deeds) likewise arises at common law. The defendant meanwhile has a common law defense to a claim for rent for the remainder of the period in a lease after an eviction for failure of the landlord to mitigate damages if the landlord does not make a reasonable effort to find a new tenant. The right to sue someone who negligently caused an accident that injured you is a common law right.
At the time of annexation of country X someone would have to decide the status of the countries citizens: If all citizens of X are now citizens of the USA, and whether they are legally citizens from the date of annexation or since they were citizens of X, and if they are considered residents in the USA since the day they became residents of X, and if they are retrospectively "born in the USA" if they were born in X. And other things, like whether non-citizen legal residents of X are now non-citizen legal residents of the USA. That has to be decided for many reasons, and the answer to your question follows naturally from this. Maybe you could check on a history site if anyone knows how this worked with Hawaii.
You don't really need any reasonable doubts about the currently available evidence to get it started. If an investigating authority thinks a crime has been committed and not yet been adjudicated, it is free to investigate, even if others disagree. There are plenty of avenues for starting an investigation: Congress can exercise its oversight power to initiate an investigation. State legislatures can do the same, so you could petition the New York Legislature, the Virginia General Assembly, or the Pennsylvania General Assembly. At both the state and federal level, attorneys general have the authority to initiate an investigation of crimes committed within their jurisdictions. At both the state and federal level, a judge's authority to appoint a special prosecutor is a power considered to be inherent in the courts, so nearly any court could appoint someone to pursue the investigation. Of course, the prosecutor's authority could be jurisdictionally limited -- if a New York state judge appointed a prosecutor, he wouldn't really have much authority to investigate federal crimes, and if a small-claims court judge in Idaho appointed a prosecutor, he'd be limited by both his lack of authority to investigate events outside his jurisdiction and the practical difficulties of enforcing a subpoena from out of state. Even at the local level, law enforcement and legislative bodies have the authority to launch investigations. If NYPD or the Somerset County Sheriff or the Arlington County Board want to investigate, they could do so. I don't know what the relevant rules are in each jurisdiction, but some states allow lawsuits for civil damages based on criminal activity. So if the gist of the sponsor's complaint is that someone used "explosives and/or incendiaries" to kill his son, it may be that he could bring a lawsuit over that, which would in turn open up the the tools of civil discovery. Of course, that's only if the claim isn't time-barred; now that we're nearly 17 years out, I'd guess that it would be too late. And there's always the possibility of continuing an independent investigation. Using the same tools that the press uses -- interviews, freedom-of-information laws, etc. -- any member of the public is free to make an inquiry into any matter of public concern. Obviously, I'd expect any of these authorities to be reluctant to take up the cause due to the investigatory consensus against the inside-job/cover-up theory, and I'd also expect -- for the same reason -- that any authority that tried to take it up would run into serious roadblocks from all the other authorities that have declined.
American citizens can have dual citizenship , but if an american citizen who has his/her citizenship renounced (even though the person was originally an american citizen) , then what is a way of obtaining the citizenship back? Possibly, by the same means that a non-citizen could be naturalized. But, immigration and nationality officials have broad discretion and would probably refuse to grant citizenship to someone who had previously renounced it. And can an american citizen without dual citizenship (Meaning that he is only an american citizen), renounce his/her citizenship? Yes. For example, Prince Harry's financee plans to renounce her U.S. citizenship and contemporaneously be granted U.K. citizenship (the paperwork goes through really easily when the Queen is your grandmother in law). Renunciation of citizenship is not necessarily tied to gaining a new citizenship, but leaving yourself stateless would be a foolish thing to do.