The devil is in the details
Verify the person was convicted of a crime, via the courts or an inmate look-up on a state's department of corrections website.
Search through the court records. If the person was charged with a felony, their case was probably handled at a county court house. It the crime involved more than one state, the case may be in a U.S. District Court. Search by the person's name. If they were acquitted, the case could be sealed or expunged. The court file should at least include a complaint from the arresting police officer, statements from victims, witnesses or the defendant themselves, and a grand jury proclamation noting which charges the defendant was indicted on.
Trace the case back to the arresting police agency or the local court that arraigned the suspect before the matter was moved to a felony-level court. If the person was acquitted and court records were sealed, the appropriate police agency may still have the old blotter entry or incident report giving a description of the crime and which charges were initially filed. The local court may still have copies of victim and witness statements before the file proceeded to grand jury.
Learn the process of making Freedom of Information requests in case the agencies ask for your request in writing. Generally, the process requires identifying the specific record you want. Agencies are not required to produce records that don't already exist. You should also ask to whom your appeal should be directed if your request is denied. Cooperation for such requests can vary by state, according to the National Freedom of Information Coalition.