Okay, let's look at a hypothetical - you say the investigation was dropped because they couldn't interview him. What is the practical difference to the investigators if they interview him and he says "I refuse to comment on anything"? There must be some way to move forward without cooperation from the accused - Assange isn't the first person to flee a country pending an investigation. Why didn't they do so?
It is unfortunately common for rape cases to go unreported/unsolved because of the lack of physical evidence. I certainly don't blame investigators for trying to interview the acused, but without evidence or a confession there's nothing for them to do.
