Earlier quoted context omitted.
And Assange kept offering to let them interview him in the UK. They refused for four years before finally agreeing last year. Why could they not have interviewed him for those four years?
Should the Swedish authorities chase after everyone they want to interview and do it where it pleases that person? If someone is wanted for rape and travels to Thailand, should Swedish prosecutor and police fly to Thailand to question them? What if the interview leads to them wanting to arrest that person, should they arrest them while in another country?
If they care about justice, and they are unable to get the person to Sweden, then it would seem the prudent recourse is to interview that person wherever they are.
You'll note that they finally did end up interviewing Assange in London, so they have conceded that it is possible and acceptable to do so. So the question is not whether or not Swedish authorities can or should do so - they've answered that question.
The question is what was served by waiting four years to do so. Certainly not justice.