No, they questioned him once (but not under arrest), after which they re-opened the rape case and upgraded the molestation case to sexual coercion and sexual molestation. They then had to go to their court and get an arrest warrant, and possibly gather other evidence (no idea what - witness statements from other wikileaks employees, maybe), by which time (around 2-3 months) he was back in London. Originally, Assange turned himself in to London police. There was then a long period of extradition hearings.
I assume the Swedish police expected him to return to Sweden when the warrant was issued, but as he did not want to go voluntarily, extradition hearings were required.
Sarah, I didn't find the word merit offensive, I just wasn't sure it was the right one but couldn't think of an alternative. Strength of the case, maybe? (have had a bit more time to think now!)
Novack, the US may well put in an extradition request in due course - perhaps the Swedish one must play out first, I don't know. Just because some states of the US have the death penalty, and Assange has pissed some people off, doesn't mean there is no case for Wikileaks to answer regarding putting troops in danger etc (I don't know about the strength of any US case either).
I would be really surprised if any US conviction did end in the death penalty, from a "PR" angle if nothing else.