Why is the prosecutor not able to question Mr Assange in the UK?

In cases where a suspect is abroad, the prosecutor must consider what investigation measures are possible under Swedish law and international instruments. Moreover, the prosecutor must consider what is required in the specific case to enable the investigation to be conducted in a legally sound and effective way without compromising quality. The prosecutor must also consider how any trial can be conducted if the investigation results in the prosecutor bringing a prosecution and how any sentence can be enforced.

In this matter, the prosecutor’s deliberations resulted in a request for the detention of Julian Assange for the crimes of which he was suspected. Pursuant to the court’s detention order the prosecutor issued a European arrest warrant

Questioning of a person in Britain at the request of Sweden would normally be carried out by the British police, who would be provided with the questions to be asked. To request the cooperation of another country's legal authorities to perform such a task is largely used when the possibility of extraditing a suspect is lacking or in interviews with witnesses and plaintiffs.

The criteria for when another country's case can be processed in Britain can be found in a publication from the British government (see link).

Regardless of how and where the questioning of Julian Assange could be performed, a case of this type would normally be expected to require further lines of inquiry e.g. the questioning of others involved. These new lines of inquiry would normally be performed in conjunction and simultaneously with the questioning of the suspect.

If Julian Assange would be questioned in London and the preliminary investigation would lead to a finding that there is sufficient evidence to prosecute Mr Assange, his personal presence is required in Sweden so that a trial can be held and any sentence enforced. Under Swedish law the defendant must be present in person at the trial in cases involving this type of crime.

Altogether, the prosecutor’s assessment is that a request for legal assistance involving the questioning of Julian Assange in London would not take the case forward in a significant manner.