He was arrested on suspicion of attempted murder.
A man, who had earlier suffered a heart attack, died at the scene but it was not clear if his death was connected to the van attack.
The incident happened when worshippers were leaving the Finsbury Park Mosque, following which one person, believed to be the driver of the van, was arrested.
The ambulance service says nine people injured in the attack were taken to local hospitals. "I don't think people understand how much these attacks affect all of us".
Khadijeh Sherizi, who lives next door to Osborne, said: "It is definitely him".
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"We managed to extinguish any flames of anger or mob rule that might have taken charge, " he told reporters, adding he was acting with "a group of mature brothers". He then said that he struck the attacker and helped to subdue him, pinning him down until the police arrived.
The London police are also investigating whether the person who died was actually killed in the attack.
The attack is the fourth terrorist incident in London in recent months.
A Scotland Yard spokesman said: "We continue to review security across London, with a focus on all places of worship including mosques and Muslim community centres". Khan also declared that British officials have "zero tolerance" for hate crimes.
"Witnesses have described hearing the van driver, who was detained by members of the public at the scene, saying he had wanted to kill Muslims".
A Metropolitan Police statement said that due to the nature of the attack, "extra policing resources have been deployed in order to reassure communities, especially those observing Ramadan".
London Mayor Sadiq Khan, the city's first Muslim mayor, called the incident a "horrific terrorist attack", which was "clearly a deliberate attack on innocent Londoners, many of whom were finishing prayers during the holy month of Ramadan".
The footage shows people screaming expletives and killer repeatedly at the man as he is held down, his face pushed against the pavement, his hair being pulled. Police killed the three attackers.