A man has been arrested on suspicion of causing arson following a fire where one person died and three were injured at a disused former hostel on Lower Clapton Road on Saturday morning.
The blaze broke out in the three storey building, believed to be used as a squat, just before 4am.
Up to 40 firefighters battled for nearly four hours before they had the fire under control at around 8am.
One man, who jumped 25 feet from a window before the fire engines arrived, is said to be in a critical condition at the Royal London Hospital with burns and injuries from the fall.
Firefighters used ladders to rescue a man and woman from the first floor. Both were taken to hospital to be treated for smoke inhalation and were later discharged.
Another man who managed to escape is uninjured. All of them are believed to be in their 20s.
The body of the person discovered in the building has not yet been identified.
A Scotland Yard spokesman said: “At this stage the fire is being treated as unexplained. London Fire Brigade will be carrying out a joint investigation with the Metropolitan Police to establish a cause.”
A LFB spokesman said that parts of the roof, ground, first and second floors were badly damaged.
The arrested man is currently in police custody.
Detectives at Hackney are appealing for any witnesses or anyone with information on the fire to call police on 101, or if you wish to remain anonymous call Crimestoppers on 0800 555 111.