Masood, a father originally from Kent, killed three people on Westminster Birdge before stabbing PC Keith Palmer to death outside Parliament, on March 22.
After the shocking attack, Islamic State (ISIS) claimed it was behind the brutal assault at the heart of Britain’s parliament.
The Amaq News Agency announced he was a "soldier of the Caliphate".
However, experts later expressed doubt to Express.co.uk after revealing the "usual" ISIS pattern was not followed in Masood's case.
In previous attacks videos have been shared with the attacker expressing support for the group and leader Abu-Bakr al Baghdadi.
However, London’s Met Police have said they cannot find links between Massod, formerly Adrian Elms, and ISIS.
How the front pages of newspapers reported the London terror attack Thu, March 23, 2017
Media across Europe, to the USA, the Middle East have paid tribute to the victims
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Police also said there was no evidence of him being radicalised in prison.
Deputy Assistant Commissioner Neil Basu said Masood "clearly had an interest in Jihad" but that extensive searches had found no solid links.
He said: "His methods appear to be based on low sophistication, low tech, low cost techniques copied from other attacks, and echo the rhetoric of IS leaders in terms of methodology and attacking police and civilians.
"I have no evidence or information at this time that he discussed this with others."