I am applying for a green card by adjustment of status because I married a U.S. citizen. One question the green card application Form I-485 asks: "Have you ever, in or outside the United States: Been arrested, cited, charged, indicted, convicted, fined, or imprisoned for breaking or violating any law or ordinance, excluding traffic violations?"
A long time ago, I was arrested in my hometown in England. I was accused of punching someone at a local pub and was charged with battery. This accusation was a complete lie and later the charge was withdrawn. Now that I am applying for my green card, I really don't want to complicate my case by bringing up the past, especially since I did nothing wrong. My question is: Can USCIS really find out about my arrest if I don't mention it?
Historically, U.S. government access to foreign criminal records (other than Canada's) has been limited. Therefore, if you do not tell USCIS about your arrest in England, there is a chance that the agency will not find out about it.
Nevertheless, given how quickly information-sharing technologies and policies can change, and how serious the consequences for failing to disclose one's criminal background can be, it would be a mistake to take that chance; especially since the type of background you have would probably not bar your permanent residence or future naturalization in the first place.
For adjustment of status applicants who have been associated with national security threats or organized crime, records of foreign convictions might already be available to USCIS through U.S. government databases and could be retrieved automatically after the biometrics appointment.
For all other adjustment applicants, USCIS would need to make an individual records request through Interpol. That's unlikely to happen unless an application raises particular suspicions. Add to this the fact that foreign governments might be reluctant to share records of arrests and charges that did not result in a conviction, and you could reasonably conclude that USCIS is unlikely to find out about your criminal history.
Still, even the remote chance that USCIS might find out about that background should dissuade you from answering "No" to the Form I-485 question about your previous arrest and charge.
Your record could be revealed, for example, if you traveled outside the U.S. one day and were required, for one reason or another, to apply for an immigrant visa in order to reenter the country. In this case, you might also need to submit a police certificate with your visa application. As a result, you would be found inadmissible to the U.S. on grounds of "willful misrepresentation"; in other words, for failing to disclose your criminal background. (And, even assuming you managed to obtain a waiver for this bar, your future access to U.S. citizenship could be jeopardized for lack of "good moral character.")
These risks seem unnecessary, especially in your case because, in the absence of aggravating factors, battery tends not to be considered a "crime of moral turpitude" (the type of crime that would make you inadmissible). And, even if it were considered such a crime, the fact that you were not convicted would strongly play in your favor; though USCIS would still want to judge for itself your explanation of the circumstances of your arrest.