Sir David Amess’ attacker may have been radicalised watching jihadi videos on the internet.
MI5 chiefs believe his killer may have been a “lone wolf” with no links to any major terrorist group.
A senior intelligence source said: “This was a planned assassination against a public figure – it has all the hallmarks of a sophisticated terrorist attack.”
They are also probing whether the 25-year-old suspect may have been inspired by the bow and arrow rampage by a Muslim convert in Norway, or if he targeted Sir David because of his links with Israel.
Counter-terror chiefs are also trying to find out the mental state of the suspect, who is British born but of Somali heritage.
The source said: “There was a high degree of planning in this assassination.
“The killer had a knife, he knew where Sir David was going to hold his surgery, and crucially he knew that there would be minimal security.
“The key questions are why this target, and why now? Was he inspired by a recent terrorist attack – such as the one in Norway?”
But the source added: “Sir David may have been targeted simply because the killer knew that he would be a soft target.”
The Southend Tory MP was a married dad-of-five, and had been in Parliament since 1983. He was stabbed multiple times while meeting constituents at a church in Leigh-on-Sea.
The 69-year-old was a member of the All Party Parliamentary Group Against Antisemitism, and a former member of the Conservative Friends of Israel organisation. It said it was “shocked and deeply saddened”.
He was also chairman of the Qatar All Party Parliamentary Group. Sources said this link would form part of the inquiry.