Hussein is believed to have been influenced by a black magic practitioner called EA Koetting, who promotes his work to more than 80,000 followers on YouTube.
Since his Old Bailey trial, it has emerged that Hussein was an active member of online forum Becoming A Living God, set up by Koetting.
The American author has associated himself with a group called Order of Nine Angles (O9A) and its US branch, Tempel ov Blood, which has been linked to a string of recent terrorism cases in Britain.
As Hussein was jailed for life for the sisters' murders, Nick Lowles, chief executive of anti-fascism campaign group Hope Not Hate, said: "Danyal Hussein was influenced by a man associated with the Order of Nine Angles before he launched his attack.
"This is yet another reason why the Government must move to ban this Nazi-occultist group.
"Bibaa Henry and Nicole Smallman had their lives stolen by this murderer, and the ideology which propelled him. Their families' lives have been devastated.
"The Order of Nines Angles' appearance in the story of these horrendous murders is shocking but shouldn't be surprising.
"We have been warning of their promotion of terrorism and sexual violence, and called on ministers to act by banning the group.
"The Order of Nine Angles is determined to promote and inspire terrorism. They must be banned."
Last week, Facebook announced that it had removed Koetting's page and Instagram account for violating its Dangerous Individuals and Organisations policies, and YouTube said a review is under way. The PA news agency has previously contacted Koetting for a response.