He would probably not be extradited to the United States if Washington asked, but it was also unlikely that he would be granted political asylum, according to a document laying out Switzerland's legal options if Snowden were to visit.
The prosecutor's office, which provided the document to Reuters, stressed the issue was "purely hypothetical" because Snowden had not been invited to come from his current refuge in Russia. It had no further comment.
The document was leaked last week and prompted a lively debate in the Swiss media.
Some German politicians have suggested inviting Snowden to Germany to testify about National Security Agency spying there, but Berlin has ruled that out to avoid a clash with Washington over extraditing him to the United States.
Michael McCaul, Republican head of the U.S. House of Representatives Committee on Homeland Security, reacted to the Swiss debate by telling the U.S.-based Foreign Policy magazine that Snowden should not be allowed to "trade our intelligence community's sources and methods for safe haven in other countries".