Is the FBI acting independently? Can the FBI indict someone unilaterally? Or do they only recommend their boss, the Attorney General, to take one action or the other? For instance, in 2016, the FBI recommended not to press charges against Hillary Clinton. Is it how it usually works (only recommendations with the AG having the final say)?
None of the above. A grand jury issues an indictment. It usually (universally?) does so at the recommendation of a federal prosecutor, who may decide based on a recommendation from the FBI. This is required by the 5th Amendment, which says "No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces...". See this DoJ account of charging, and this broader FAQ on federal indictments.
None No law requires police to keep people apart when making statements. Doing so is good police practice. In some police organizations internal regulations or procedures may specify that officers should do so. But those are not laws. In some cases witnesses may have had a chance to confer and agree on a story before police arrive, the police cannot prevent that. The trier of fact can take into account that witnesses had a chanc to agree on a false story.
If I were a DA (District Attorney) looking out "stamp out" statutory rape, I would make the rounds of the hospitals, identify women who gave birth, or were impregnated when underaged, and go from there. But few, if any DAs, do this. No, you wouldn't. First, you have neither the time nor the budget to do this. Second hospitals are not public property, you would need a warrant which the court won't give you because you don't have probable cause to believe a crime has or is being committed. As a DA, I would of course, follow up on any complaints lodged by the victim, or even by her/his parents. And maybe I would prosecute a case where people were "caught in the act, or there were nude pictures, etc. May even an especially egregious PDA (public display of affection). No, you wouldn't. You would follow up on complaints to the extent that you have the time, budget and manpower to do so and you would prosecute cases where you believe that you have a reasonable prospect of getting a conviction and where prosecution is, in your opinion, in the public interest. In the real world, that means where the police hand you a brief of evidence that is a lay-down misere and (for statutory rape) where there is a real power imbalance between the perpetrator and the victim - giving 2 willing 15 year old kids the label of 'sex offender' for life is probably not in the public interest. But suppose there were no complaints or smoking guns. Could someone investigate based on something like a teenager "holding hands" with someone much older? To make the question objective, what has historically caused DAs to prosecute people outside of the above parameters? With some exceptions, it is not the role of the DA to initiate or conduct investigations of criminal actions - that is the role of law enforcement officers, usually for this particular crime, police officers. Notwithstanding, the general rule in western, liberal democracies (which the United States, with a certain generosity of spirit, can still be considered) is that citizens are allowed to get on with their lives without day-to-day interference from the state. That is, law enforcement officers do not 'go fishing' for crimes, they investigate crimes that they have a probable cause to believe have actually happened, either because they themselves saw it happen or someone has reported it to them as having happened. The term for having a law enforcement officer following you around waiting for you to break the law is 'harassment' and may itself be illegal. A law enforcement officer can initiate an investigation based on anything but as no law enforcement agency has unlimited resources, they tend to follow only those investigations that might lead somewhere. For example, it has been known for parents to hold the hands of their children and even to publicly display affection towards them and parents are often "much older" then their children - this would not generally be grounds for initiating a statutory rape investigation.
If the DA decides to press charges (we don't know) and if he is convicted (looks like a solid case), the problems are not just the sentence itself. There might be a probation period with conditions like drug tests and counseling, with penalties if he misses them. It is legal to discriminate against people based on prior convictions. While California has some restrictions on when employers may ask, they can make it one part of their assessment.
When it is a mistake of memory, and not intentional (as this question is asking), there are no clear standards, and it is largely up to prosecutorial discretion. This means that whatever factors affect prosecutorial discretion (such as the prosecutor knowing who they have to work with on other days) can become significant in the determination. A prosecutor who announced this decision also specifically noted that it's up to the prosecutor to decide each case separately, with no guidance on fact patterns that could influence the decision either way. The Washington Post Magazine covered this question somewhat in depth several years ago, arriving at that conclusion. This was a surprise to me, but the article seems like a good resource on this - the question turns out to be more interesting and less resolved than it first appeared to be.
So each government has jurisdiction of the crime if and only if it occurs within their borders. In addition, the Federal Government can take a crack at any crime any where in the United States, though typically they only do so if the crime involves crossing state lines (kidnapping over state lines, ect). At the maximum, suppose for arguments sake Alice fatally shoots Bob while Bob is standing at dead center of the Four Corners Monument (the only place in the United States where four states meet). This means that one act of Murder has been committed in four seperate states, so Colorado, Utah, New Mexico, and Arizona can all claim jurisdiction over the case and each prosecute Alice for First Degree Murder. Additionally, the Federal Government may step in and also prosecute Alice for First Degree Murder (though they are more likely not too. The Feds rarely prosecute crimes after the State UNLESS the State did something horribly wrong... I.E. Utah let her go because Utah is crazy). Additionally, the monument marks the dividing line between the Navajo Nation and the Ute Tribe, both semi-autonomous Native American Tribes that have their own recognized court systems, so they could conceivably charge Alice with First Degree Murder. So in total, the most amount of times someone can be charged for the same crime due to cross-jurisdiction is 7 times (Four States, 2 Tribal Governments, and one Federal Government). In likely hood, a few of these guys will pass because it's a waste of effort. If Alice gets the death penalty in Arizona, Colorado can't kill her a second time. It's important to note that each government gets exactly one trial so Alice can't be convicted twice in Arizona. A more realistic example occurred in the D.C. Beltway Sniper Case, where the perpetrators were tried in both Virginia and Maryland but only for the crimes committed within those states. VA got first crack because they had (and eventually carried out) the Death Penalty. Maryland tried both for insurance in case the VA cases got thrown out for reasons. The Feds found this satisfying and decided not to press their charges.
If the prosecutor (P) knows or strongly believes based on this new evidence that A is innocent, ethically P should start proceeding to have A's conviction reversed or reviewed. But in far too many cases P does nothing of the sort. If P simply files a charge against B and proceeds to try B for the crime, P leaves it open to B's Lawyer to ask &quot;Didn't you already convict A for this crime? what about that?&quot; as part of a defense, which might well embarrass P and lose the case. So P may well choose to file charges against B claiming that A &amp; B acted together as accomplices, even if this requires misstating the evidence, or suppressing part of it. Or, P may simply ignore the new evidence, leaving A in prison and B free. This is unjust, but requires no effort on the part of P, and may seem less likely to raise embarrassing questions about why P got the case against A wrong. P can always claim that s/he did not believe the new evidence. That might even be true, there is such a tendency to believe what we wish to believe. The relative frequency of these responses on the part of those in the position of P here is really not possible to asses. The last two responses involve P suppressing or at least burying relevant evidence, and unless it is brought to the attention of others who publicize it enough that action is taken, it will not be generally known and cannot be tabulated in any statistics. P's office will certainly not respond to any survey which asks &quot;How many times this year did you suppress the true facts to leave in place an unjust conviction you had previously obtained?&quot;
If you state, to a third person, that Joe has performed a criminal act then that is defamation and you can be sued. Unless it is true. However, if you are relying on the truth as a defence you will need to provide evidence that it is. At the moment you lack: a criminal conviction of Joe any physical evidence against Joe any personal knowledge that Joe has committed these acts. All you have, is second hand rumours that this has happened to 5 women, some of whom have reported it to you in person. This is called hearsay and it is not evidence. It may be true, it probably is true - you can't prove it's true and in court, that's all that matters. If you were sued your only possible defence is to call these women to give the evidence they are unwilling to give - are you willing to betray their confidence to that extent?