"The attack unfolded whilst a man was already receiving first aid from public at the scene, and sadly that man has died. Any causative link between his death and the attack will form part of our investigation," Basu told reporters.
The suspected perpetrator has been arrested on suspicion of attempted murder, he said.
"It is too early to state if his death was as a result of this attack," Basu said of the incident that he said "bears all the hallmarks" of a terrorist attack.
Police are determining whether the tragic incident was a terrorist attack, UK Prime Minister called the Finsbury incident a "potential terrorist attack."
The Muslim Council of Britain said that the attack was directed at Muslims leaving Ramadan night prayers.