Jihadi John, the man who was harassed by authorities until he broke and turned into what the authorities accused him of being.
Unlikely, though it is the myth put about by the like of CAGE. What is more likely is that the severe blow to his head damaged his frontal lobe on that side with the consequences that are well known, including psychopathy. Hence the brutal and terrifying deaths of so many innocent civilians in the desert, whose well being you conveniently skate over with your weak argument. Moreover, even without evidence of cranial trauma, it is necessary to ask what his premorbid condition was prior to being recruited, it being highly abnormal that a supposedly 'beautiful' 'gentle' young man would turn into a psychopathic murder, or do you claim that there was absolutely nothing deeply pathological about his behaviour?
To attribute his bestial violence to investigations by the authorities is, to put it kindly, utter piffle. Many untruths have been told about their interventions. The British int & sy services were checking and approaching all individuals showing the same signs of interest in terrorism, because failure to do so in the past led to people's throats being slit, tall buildings falling, buses and tube trains exploding, and British soldiers heads being removed on the streets of their home country.
Your claim represents to me the most odious and truth avoiding of inflammatory political correctness, and it is the sort of loaded disingenuousness that has led to young girls suffering in Rotherham, never mind the vicious deaths of people like Ken Bigley, who sought only to do good, for whom even the murderous Al Qaeda spoke defensively.
As an ex soldier who was treated very badly in this way by civvies from the politically correct wing of society the only apposite thing that I can say is that I hope you never rely on British service personnel to haul your arse from out of the fire. Because I know they will be as reluctant to help you as you have been to admit the truth.
 It being a recorded fact, backed up by statements from his age cohort that his personality changed from that moment on.