It is impossible to know if he has actually committed an offence until he's been tried and convicted. That is not the standard in ANY extradition, be it this or mass murder. What you have to be is accused of an offence that is an offence in the country you're being extradited to, and an offence here, and one that, if convicted, carries a maximum sentence of at least 12 months.
Yes, he is. But the UK authorities have not (yet) elected to prosecute. They could, but so far, have not. Why this is you'd have to ask the CPS, but it may be that they do not consider it a priority, perhaps because the main victims were in the US.
That's the whole point of extradition - to return people accused of offences in foreign lands to stand trial before a court in that land if the criteria of the Extradition Act are met. And a judge here has ruled that they were.
As I have said repeatedly in this thread, you cannot be extradited unless the offence you are accused of in that foreign land is also an offence here (carrying a potential sentence of at least 12 months, so it doesn't apply to a vast array of more minor offences). It's a principle called 'dual criminality' and is one of the issues settled by the judge. The ruling is that what he did is an offence here. That, of course, could be overruled by a superior court if it goes to appeal and he wins, and the extradition has, as I understand it, yet to get the sign-off of the minister. But the extradition was challenged in a court, and so far at least, the ruling of a judge is that what he is accused of, and there seems to be little doubt he actually did what he's accused of, did constitute an offence here too. If it did not, the extradition would not meet the legal criteria and would have been rejected.
So who doesn't get it?