He based his life on the Leonardo DiCaprio film Catch Me If You Can, in which a teenager cons his way into jobs. Williams watched the film multiple times. He also posed as an ambulance officer, counsellor, pastor, lifeguard and cancer survivor.
He even stole a plane - starting it up, taking it out of a hangar and taxiing up and down the runway at Motueka while talking to other pilots on the radio system.
Police said he was "very plausible, very convincing".
In court yesterday, Judge Richard Russell told the teenager there was nothing smart or clever about his offending.
"You are cunning, you are manipulative and just plainly dishonest. And you have little regard for the victims of your offending."
Williams' former flight instructor David Marriott said the teenager was "dangerous".
"He could steal an aeroplane ... absolutely," he told One News.
Last month Williams' father, Warren, told TVNZ's Close Up his son was not dangerous and had "pulled off some pretty amazing things".
"There are a lot of people who can't pull off their socks without help ... The more that it happened the more he got away with it and the bolder he became," Mr Williams said.
"His motivation is to be looked up to and to be this adult figure of authority and importance."
Mr Williams said he believed his son could be an asset to society if he used his "talents and skills" for good.
