I thought you said he had to have an interview in Sweden to comply with Swedish legal requirements, now you are saying that it is not required, but a requirement of that particular prosecutor, and that other suspects have been interviewed about criminal matters overseas.
From what I understand there are several things in play here:
1. It's not just about an interview, it's an interview in the final stages of an investigation, and one that is supposed to lead to JA being charged.
2. It's possible for a prosecutor to interview a person outside of Sweden (I have seen reports of that), but the suspect need to be in Sweden to be charged. The examples I've seen described was not about interviewing for charging, it was the first interview in an investigation. That first interview with JA happened early on in the investigation.
3. Interviewing outside of Sweden is at the the prosecutors discretion, and the prosecutor has decided (as is described on the Prosecution Authority Homepage I linked to) that they need JA in Sweden to be able to complete the final stages. This might for example involve re-interviewing other people based on JAs statements.
4. The arguments on why JA was needed in Sweden that the Swedish prosecutor gave to the English courts was enough to satisfy them that the request for extradition is legal.
5. JA promised to come back for an interview, he didn't come and instead has taken every action available to him to try to avoid getting extradited to Sweden. There is nothing that says that says that interviewing him in the Ecuador embassy would move things forward. It might even be make JA even less disposed to come to Sweden.
Compare for example with what is claimed about the US - the claim is that the US has a Sealed Indictment for JA - from what I understand (but please do tell me if I have misunderstood), the reason for having a
sealed indictment is to make it easier to apprehend the person - you don't want the person so suspect that they will be arrested.
(Now, it seems that JA is already as suspicious as a person can be, so I'm not sure what value it is to keep it sealed?)
Now, if you transfer the same thinking to the Swedish situation. Today JA seems to expect (or at least claim/home for) that Sweden will drop the case if they just interviewed him again. If he gets the understanding that he definitely will get charged, why would that make him more willing to go to Sweden compared to the current situation?