In some cases, when a crime occurs in the US or affects the US and will be tried in a US court, authorities and law enforcement agencies need to speak to witnesses who are not in the US at the time. In some cases, such witnesses are needed at trial. The US allows law enforcement agencies to file USCIS Form I-854 (Inter-Agency Alien Witness and Informant Record), which grants “S” non-immigrant classification to non-US informants and witnesses. This classification allows these informants and witnesses to enter the US in order to assist police, authorities, or to testify in a court of law.
Number of pages of the form: 10 (Form is 6 pages and instructions are 4); this form can only be filed by police or enforcement agencies, not by the general public.