I strongly suspect that standards of evidence and due process in a Vietnamese (i.e., Communist) court are not at the level of those in the USA or the UK, and I hope that his case is closely followed to ensure that he gets a fair trial. That said, if he did have sex with a 12-year old girl...may G-d have mercy on his soul.
He did it multiple times in the UK and did time for it.
Then, as soon as he was released, he decided to relocate permanently in Southeast Asia - the world mecca of illicit sex tourism.
As far as I see it, he is owed a bullet for the previous offenses anyway.