The marriage itself won't trigger anything with immigration, since immigration agencies have nothing to do with that kind of thing. It is not clear from the facts you've given if he has a legal status here or not. If he does not have a green card and you are a U.S. citizen wanting to petition for him, it is important to speak with an immigration attorney first. Before you file anything for him, a lawyer needs to review his criminal history to make sure it does not make him ineligible for a green card. Many crimes have immigration consequences, which can vary. The lawyer will also need to review his immigration history to determine what effect that may have on his options.
The information offered is general in nature and not meant to be relied upon as legal advice. No client-attorney relationship is created through this information. Please consult an attorney prior to making legal decisions.
Are you saying that he did something that resulted in a 23 year prison sentence?
If so, they probably have him on the 'radar' and don't need to put a hold on him at this time.
The marriage request won't 'flag' him ... but I bet that immigration knows about him.
Talk to a lawyer, his crime must have been super serious and he probably won't be allowed to stay in the US ... even if he marries a US citizen.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
You need to consult with counsel that can carefully look at case perhaps there is a possibility he is a citizen due to his father's citizenship. If not unlikely to adjust if he did along prison sentence!