According to the letters, obtained by NBC News partner Aftonbladet, the U.S. special presidential envoy for hostage affairs wrote to Swedish prosecutors urging them to release Rocky.

“The government of the United States of America wants to resolve this case as soon as possible to avoid potentially negative consequences to the U.S.-Swedish bilateral relationship,” Amb. Robert O’Brien wrote in the letter, dated Wednesday.

In response Sweden’s prosecutor-general, Petra Lundh, defended the independence of Swedish courts and said she therefore had to deny O’Brien’s requests.

“No other prosecutor, not even I, may interfere with a specific case or try to affect the prosecutor responsible,” Lundh wrote in a letter dated Thursday.