The Form W8-BEN is kept for your records. It is equivalent to a Form W-9, Request for Taxpayer Identification Number and Certification, that is given to U.S. persons to certify that they are not subject to withholding.
You must keep adequate records to verify that the individual only performed work as a foreign person in Switzerland and not the United States. However, if the individual is considered a United States citizen or a resident alien, he must report his worldwide income no matter where the work is performed.
