The murderer of schoolgirl Milly Dowler turned Muslim while in jail in 2011 and began calling himself Yusuf Rahim.
He is one of a huge number of lags allegedly enjoying benefits including better meals, as part of the transition.
Bellfield reportedly eats only halal meat and prays to Allah five times a day at Durham's Frankland Jail.
It comes amid a surge in Muslim inmates in recent years, with one in five of those serving sentences in Britain's maximum security jails now said to be following Islam, according to union officials.
The Prison Officers' Association has put that down to thousands of lags becoming so-called "convenience Muslims" - converting to the religion to deliberately play the system.
A report into prisons five years ago, called Muslim Prisoners’ Experiences backed that up when it said those in jail see “perks” in converting to Islam, including better food and protection.
It added they were also being made even more vulnerable to radicalisation.
Bellfield was jailed for life in 2011 for murdering the 13-year-old in 2002 and killing Marsha McDonnell, 19, and Amelie Delagrange, 22, as well as attempting to murder Kate Sheedy, 18, in 2004.
The 47-year-old is suspected of carrying out over 100 rapes.
But Bellfield, like some others, changed his religion to save his own skin, and get a better life behind bars, sources claim.
In a recently published letter to a journalist, Bellfield said of his new-found religion: “Reference my Muslim status, this is between me and the almighty Allah.
“Maybe one day, you will find this beautiful faith.”
When he originally converted, staff at Wakefield prison, in West Yorkshire, said he was out to to impress the Muslim extremists who have given him a hard time while he has been incarcerated there.
A prison insider also said it was "generally accepted" that Halal food was better than other meals.
Speaking to The Mirror, a prison officer said: "Bellfield is doing this for better meals and a cushier life. He has the right to pray five times a day so it gives him a break.
Posted by Women Against Shariah on Wednesday, February 17, 2016