How could he get naturalized with a criminal record? There is no way that he walked free from the firebomb case. 
EDIT: A search on the Judicial Yuan database shows that “Paul” has 4 convictions and is as recently as August 2016 listed as “British national” in court documents. I doubt he was actually able to naturalise and become a ROC citizen - regardless of what he claims. In fact, in his latest case (105年度訴字第118號 for anyone who cares to look it up, it’s public information under ROC law) the judge even orders him deported. I am really not sure why he is still here.
EDIT 2: The Taiwan High Court overturned the District Court verdict in March this year and ordered “Paul” to undergo psychiatric counseling. Hence no deportation. The High Court verdict still mentions “Paul’s” nationality as UK however. Case number is 105年度上訴字第845號 for anyone who cares to read it.
@Mods: I am not sure whether the details in my post violate forum policy. I am not revealing Paul’s Forumosa ID, I am merely posting publicly accessible information maintained in the Judicial Yuan database.