I've just been googling why my force was using an AS350 a couple of weeks ago (wondering if some forces might revert to older/other models pending AAIB) and I came across the police aviation page.
Curiously, I read one helo was brought down by a defective fuel pump.
Wasn't on a 135, but it's another possible surely, apart from main gearbox failure or "did it run out of fuel" as I saw one person quote on another forum.
Just wondering aloud, as the 135 isn't exactly plagued by mgb stuff like the 335.