London: Detectives are trying to establish what drove a man to allegedly go on a rampage and behead an 82-year-old woman in her garden on Thursday, while a monitoring group said the incident had already led to a spike in threats to Muslims and mosques.

A 25-year-old man suspected of attacking Palmira Silva in Edmonton, north London, is under guard in hospital after being subdued by police, who used a Taser.

The incident caused panic in the area as the man allegedly attempted to attack at least two other people, while armed with a machete. According to residents, he was heard muttering about cats, which he also is said to have attacked that day.

Police insisted that the alleged murder of Silva was not connected to terrorism, but a group monitoring threats against British Muslims said it saw a rise in reports within hours of the news breaking. Fiyaz Mughal, director of Tell Mama, said the incidents included threats in the street to women wearing the hijab in Wales and south London, and threats on social media.

Mughal said of special concern was that the threats had changed to naming specific targets, including a mosque.

Mughal said: “The assumption is ‘beheading equals Muslim’. The association, for some, is an automatic response.”

He said his organisation had seen three spikes in threats in a fortnight: after an official report into sexual abuse in Rotherham perpetrated by Muslim men; the release on Tuesday of a terrorist murder video showing the beheading by Islamic State of Iraq and the Levant (Isil) of an American hostage, and now after the alleged Edmonton attack.

Mughal said the nature of many threats on social media had changed: “They are not saying ‘we hate you’ or ‘we hate Muslims’, but [are making] actual threats of attacks against Muslims and mosques.”

The nature of the alleged killing, coming 48 hours after the beheading of US journalist Steven Sotloff by Isil militants, led to early speculation. One newspaper report claimed the suspect was a Muslim convert. But police stressed the lack of a terrorist connection in three separate statements.

The investigation is being led by specialist murder detectives, not by Scotland Yard’s counter-terrorism command. There was no suggestion from witnesses that the alleged attacker said anything related to religion, as happened in the 2013 murder of the soldier Lee Rigby in Woolwich, south-east London.

The Barnet, Enfield and Haringey mental health trust, which covers the area of the alleged attack, declined to say if the suspect was known to them.

More eyewitness accounts of the incident continued to emerge, alleging that a man ran across gardens and hacked at the victim, with police smashing windows to pull people to safety and risking their lives to distract the attacker, saving others from harm.

Myrvin Kirwan, a cable TV installer, said he came within feet of the alleged attacker as he was working in a house in the area: “I looked out through the glass doors into the back garden and then I saw him bloody hands, machete, and no shirt.

“The customer shut the door, then the police came in saying ‘Get out of the house, get out of the house’.” He said of the suspect: “He was looking through me.”

Police declined to discuss a report in the London Evening Standard that named the suspect and claimed he was interested in cage fighting and had been living temporarily at an address near Silva’s home.

The victim worked at a nearby café. Lucie Fabry, 26, said: “I heard what had happened last night, then saw the paper this morning and thought ‘It’s the lady from the café’. “We all knew her as Pam. She worked there, that was her life and soul; she was always in there, bless her.”