Bellfied was jailed for life over the murders of Milly Dowler, Amelie Delagrange and Marsha McDonnell between 2002 and 2004.
Several women have come forward to claim they were also attacked by Bellfied after the drama Manhunt was shown on ITV last week.
The Met Police has not confirmed how many allegations they have received, but has said they will be assessed by a team from its child abuse and sexual exploitation command.
Manhunt was based on the book of the same name by Colin Sutton, who was the senior officer in charge of the investigation into the murders.
He told Sky News: “Logically you don’t wake up on your 35th birthday and say ‘I think I’ll start murdering people’.
“Criminologists will say there’s a progression often, an escalation in crimes that people do, and they start small and get bigger.”
He added: “I’m sure this a man who has been committing offences and assaulting people for years and years.”
The former detective chief inspector said women have contacted him directly on social media since Manhunt was aired.
He added that he has passed their allegations on to the Metropolitan Police.
Mr Sutton also told Sky News about his experiences of Bellfield after his arrest.
He said: “I didn’t speak to him an awful lot, because he was quite rude and unpleasant to me every time I met him.”
Mr Sutton added: “He would just do what he wanted to do, to satisfy his desires or his needs at that time.
“Without any reference, or any thought for any others – be that his partner, his family, the public, the law.
“I’d never come across somebody who combined that sort of disregard for other people, with the propensity to serious violence.”
Mr Sutton and his team had to watch around 2,500 hours of CCTV in their efforts to catch Bellfield, and were confident that all three murders were committed by the same person.
He said: “This quiet, safe corner of London, was suddenly the sight of murders and murderous attacks on women.
“(We thought) these crimes are so similar, we thought the chances of them being carried out by two people are so remote, it makes perfect sense for them to be investigated by the same team.”