Legal Question in Criminal Law in California

First of all, how sure are you that your loved one isn't who he claims to be? The death record you saw could belong to someone who had the same name. Or it could be incorrect. You should look into these possibilities if you haven't already.

Even if you're right, I don't think you have a duty to turn him in or to show anyone what you've found. But you probably have a duty not to vouch for his identity now that you know it's false.

Living under a false identity isn't necessarily a crime in its own right. But it would be hard to do without committing a variety of other crimes along the way. Your loved one may also be trying to hide from the law, if he's wanted for crimes he committed under a different name. It's also possible that he has less sinister reasons for assuming a new identity.

I'm going to intentionally be a little offensive here, but what on earth makes you think you have any right to meddle and intrude on this person's privacy just because of some relationship to him, or to slander him as being a criminal if you 'report' him?? You already admit he "does not have a criminal background" in this identity, and lives an apparently blameless life.

You have not stated what credible evidence exists to support your conclusion that his is a 'false' identity, other than your conclusion. Even if true, so what?

What on earth makes you think using a name of his own choosing is a crime??

Even if this is a false identity, who told you there is any terrible crime in doing so, or any crime that induced him to do this 30 years ago? Even if there was a long ago crime, the statute of limitations ran out decades ago, unless the crime he committed was murder. If that is the crime, then report away if you choose and if you think this is the moral thing to do.

You have no legal 'right' to meddle, nor legal 'obligation' to report people to authorities - people who apparently have not harmed you or anyone else.

Telling in your post is that you haven't even demonstrated the courtesy of giving this person the opportunity to admit, deny, or explain before you run off and possibly damage his life.