In countries where the law is still observed, it is usually not possible. In order to have rights, you need to be someone. To have an identity. What an identity is, is defined by law. Pseudonym identities are very rarely legally possible. So your answer is No.

But if you are inside Usa (probably true because of your lack of saying it) then simply everything is possible, since they don’t have the rule of law anymore.

I asked a lawyer this once. After he was done laughing, the gist was that the limits of anonymity for witnesses is damn near zero. There’s circumstances where a witness might be given some cover if they’re minors, adults just don’t get that. That’s the US though, there are places where secret or anonymous testimony is used.

Now, the conversation did include some hypotheticals. He said there could be some arguments akin to what some vulnerable populations occasionally get, or when a witness is in immediate and provable danger. Anonymous testimony as a last resort is possible, just so rarely given as to be laughable in his opinion.

The big factor in why it wouldn’t work for a vigilante is that even when anonymous testimony is allowed, it’s really only anonymous to the courtroom. The judge would have to know who it was, and likely multiple people involved in the process of trying to get the judge to go along with it.

Even then, a U.S. based prosecutor would be desperate to even consider trying in the first place. Anonymous testimony would be easy to counter, and there would be a ton of ways to counter the attempt in the first place.

What I was told is that it would be career suicide to try and fail. And the chances of success for an adult vigilante are essentially zero when the difficulty of making it happen under very rare circumstances for kids or known adults is already difficult.

There would need to be legislation in place for it to happen in the real world in most countries. I did a quick search on other places, and it’s still rare even in places where secret testimony is less rare than the US. Even those places, the identity is known to the state.

This actually did happen in Seattle, Washington. There are quite a few real life “super heroes” that dress up and patrol their respective cities. This one was named Phoenix Jones and he had the whole comic book hero costume and everything. There was a law that allowed people to fight as long as both people consented called Mutual Combat and that played a big into allowing him to do what he did.

But he did end up being pulled into court and they forced him to de-mask himself and reveal his true identity. He even had an “origin story”, though not as dramatic as something like Bruce Wayne, but still. He’s an interesting character to look into.

Consider my comment as just a brief summarization of this whole thing as an answer to your question.

I think this depends on which region the court is in, but like in the US, if the hero is the defendant or plaintiff, I don’t think any court would allow the hero to remain masked and without showing their identity. Best they could do is only reveal to some parties involved in the court case, but the identity is still exposed. I think the only exception may be if the hero is a witness, and even then, maybe not and would need to identify to some involved in the case. This is because many courts around the world require people to know who their accuser is and lawyers often will try to fight against this since a secret identity cannot be truly verified for the best results in a court determination.

It’s important to note that once in court to testify, they’re going to investigate anyone testifying.

Both the prosecution and the defense. Depending on whose witness they are, one would be investigating to make sure you’re credible and the other to hopefully find something to discredit that.

Further while vigilantism is not necessarily illegal on its own, it’s generally (almost always,) going to involve other crimes.

Vigilantes do not have privileged arrest powers, so at best one is going to have to either work a case (legally,) and then turn things over to cops, or do crime (best the shit/kill the bad guy and pray they got it right.)(they probably haven’t.)

This means that by the time a vigilante takes the stand; they’ve done crimes and even if the entire system lets you … you’re gonna get arrested.

The only way out of that is to get outed and get immunity.

All of that said, if you were a bystander and not necessarily involved, you might be able to testify as your identity and not alter ego. You would have to explain what you were doing there, though.

And you’ll still be investigated… and probably found out.

Depends, I would assume, entirely on where we are and which judicial system applies. Not every jurisdiction allows the media to publish the name of every accused person.

Edit: I may have misunderstood the scope of the question.

I have this vido on my to “watch later” list since 2016 or so. I didn’t watch ir yet, but it seems to be about exactly this problem: https://youtu.be/h846qvlP26A

A year ago, I had this fun comment about if necromancy were possible in a courtroom setting. And I think the follow-up is relevant here:

TL;DR: rules of evidence would still apply to the undead, and judges must take care to balance the probative value of evidence with any prejudicial quality it may carry. (to be abundantly clear, this was a schittpost lol)

even when you have a live body on the stand about to give testimony, it is essential to lay the foundation as to who they are and their legitimacy.

If a masked vigilante’s legitimacy as a vigilante cannot be proven independently – a tough act since they would want to maintain their secret identity, coupled with the possibility of copycats or false flag operatives – then a jury or the bench would be reluctant to give their testimony much value. It’d be no different if you or I waltzed into court and proclaimed to be the world’s foremost expert on bitemark analysis and underwater basket weaving, but that you just have to “trust me, bro” on that claim. No reasonable person would believe that claim.

Now, your question focuses on whether a masked vigilante can testify but with a proviso to protect their interests. To that question, the answer is: maybe. Sometimes a witnesss (eg FBI Special Agent) can have their identity protected being exposed in open court, but still allow all parties (clients and their attorneys) to know the witness’s identity, for the purpose of fact checking. While there’s a fairly strong interest that trials be mostly open, a Special Agent’s identity should generally be protected, since that could be the very essence of their occupation.

And you could maybe say the same thing for a masked vigilante. But in the opposite, one could argue that the general public has an overwhelmingly strong interest in learning the identity of a masked vigilante, which might suggest that the court deny the vigilant the benefit of a private testimony.

Still, the vigilante could proceed to give testimony, unmasked if so needed. However, if the question was tweaked to be “can a court force a masked vigilante to testify, and thus reveal their identity?”, the answer in USA law is no.

Specifically, the Fifth Amendment guarantees that no one can be forced to testify if the testimony can be used against them later. So either the testimony isn’t taken at all, or that they are immunized for anything that they testify about. Those are the only two remaining options that satisfy the 5th Amendment. And so, since a masked vigilante would have potential criminal liability for past crimes, the government (federal or state) cannot force them to answer questions on the stand, without first granting immunity. If they offer no immunity, the vigilante can simply reply that they’re invoking their right from the 5th Amendment, and no harm can come to them for doing so; being harmed for invoking a right would make said right into a meaningless thing.

But if the prosecutor decides that it’s super important to hear what the vigilante has to say, then they can grant immunity. Unlike a pardon which is a gift that a person can choose to decline, immunity is unilaterally granted, and the recipient cannot reject it. Once that’s done, someone can be forced to testify (eg locked in jail until they will talk), since there is no longer a risk of the testimony coming back to harm themselves later.

Note: those words could be entirely damning to somebody else, and there’s no such thing as “third party Fifth Amendment” rights. This is almost always the reason why the prosecutor would grant immunity, to get the compelled testimony from underlings or witnesses necessary to convict a bigger target. If a masked vigilante was the only witness to documents about accounting fraud, which were later burned, that could be really useful when trying to pursue white collar crime, even if the cost is to give up any possibility of prosecuting the property damage crimes that the masked vigilante may have committed.