The attacker, who is believed to have acted alone, struck as the area was busy with worshippers attending Ramadan night prayers at the mosque.
Mamhoud was joined by several other bystanders who formed a protective ring around the suspect until police hustled him into the back of a van, the Evening Standard reported.
An imam reportedly saved the van driver involved in the suspected Finsbury Park attack from being attacked by members of the public in the immediate aftermath of the crash.
British Prime Minister Theresa May vowed yesterday to fight terrorism in all its forms after a white driver ploughed his van into a crowd of Muslims in a suspected Islamophobic attack. The council called on the authorities to increase security around mosques.
The site of the incident is close to another mosque near the Finsbury Park on the same road.
Suspect appeared to blow a kiss at onlookers after being put in a police van following the incident.
May, who was heavily criticized for failing to meet survivors of a devastating fire in a London tower block last week, visited Finsbury Park Mosque where she met local faith leaders.
One man was pronounced dead at the scene and eight others were taken to hospital. It has not been associated with radical views for more than a decade. "All my thoughts are with those who have been injured, their loved ones, and the emergency services on the scene".
Those attacks and a third outside a pop concert in Manchester have triggered a surge in hate crimes against Muslims around Britain. On Monday the police said that the victim was already being treated by emergency services when the attack happened.
London Mayor Sadiq Khan said "terrorism is terrorism".
"These people who have been attacked were the people who just left the mosque ... but we don't know whether they are all from the Muslim community - I assume that there are other casualties and victims who maybe are not even Muslim".
Imam Mohammed Mahmoud told Sky News how he had just finished prayers when a "panicked" worshipper ran in to say what was happening outside.
The Metropolitan Police said they "responded instantly " and armed officers were on the scene within ten minutes.
Residents near Cardiff said they were "shocked" after seeing photographs of their neighbour arrested in London.
"Like the bad attacks in Manchester, Westminster and London Bridge it is also an assault on all our shared values of tolerance, freedom and respect", he said in a statement, referring to attacks in previous months.
"There has been an outpouring of sympathy for all for the recent terror attacks but hardly a whisper on this attack", he said.
The author's commentary had a common theme: To her, there is a notable double standard of how people react to terror attacks carried out by Muslims as opposed to those of another religion.