The former police detective has been making a follow-up programme to his original ITV1 documentary into allegations that the star sexually abused vulnerable teenage girls.
He told the Radio Times: “In the previous programme it was unclear what came first.
“But I can very clearly tell you now that he created his television series as a vehicle for his offending.
“I believe he engineered his programmes within the BBC and Radio Luxembourg in order to gain access to children.
“The classic examples are Top Of The Pops, Savile’s Travels, Jim’ll Fix It - all of them gave him access to young children. That’s why there were so many victims.”
He told the magazine of the follow-up documentary: “In the first programme, we focused on a fairly short time scale. Now we’re able to show that Savile’s offending behaviour spanned four decades and many hundreds of victims.
“This isn’t just someone who offended only against 13, 14 and 15-year-olds. It’s someone who offended against ten-year-olds.”
The second programme, Exposure Update, investigates the full length of the TV star’s four decades of abuse, from Radio Luxembourg in the 1950s, where he presented the Teen and Twenty Disc Club.
The documentary also looks at how Savile got away with his abuse for so long, and whether the establishment turned a blind eye.
Mr Williams-Thomas, who was due to be part of the original Newsnight investigation which was abandoned, admitted he was wary about the involvement of compensation-seeking lawyers, because, he said, people might wrongly begin to question the victims’ motives.
He said of the victims that he had spoken to for the new programme: “They don’t want a penny from Savile. They just want the truth to be on record, to be listened to, to be believed.”
He said of the BBC, which has been in crisis since it emerged its Newsnight investigation was shelved: “To me the focus was never the BBC, it has always been Jimmy Savile as the offender. This was a man who made it his hobby to open up every single door that he could. At the height of his fame, there wasn’t anywhere he couldn’t go.”
He added: “I think there will be further arrests over the forthcoming days, weeks and months of people who were party to offending alongside Savile.”