Detectives continue to appeal for information and witnesses after a man died following a fire at a block of flats in Hackney.
Police were called at 14:38hrs on Wednesday, 18 May, to reports of an explosion and fire at the flats in Stamford Hill, Hackney, N16.
Officers, the London Fire Brigade (LFB) and the London Ambulance Service (LAS) attended the scene.
A 30-year-old man, a 29-year-old man and two 28-year-old men were found with burn injuries. All four men were taken to London hospitals.
The 30-year-old man was later transferred to a specialist burns unit in Essex but died at 22:27hrs. His next of kin have been informed. Formal identification and a post-mortem examination will take place in due course.
The 29-year-old man and one of the 28-year-old men have been transferred to specialist burns units in Sussex and Essex respectively. Both remain in a critical condition.
The second 28-year-old man was discharged from a central London hospital on 19 May. He was arrested on suspicion of involuntary manslaughter and allowing a premises to be used for the production of class B drugs. He has been bailed to a date in mid-June.
Detective Inspector Paul Ridley from Hackney CID said: "An investigation has been launched to establish the circumstances of this incident. I am asking anyone who can provide any further information, who witnessed the explosion or the immediate aftermath to contact my investigation team."
Anyone with information should contact Hackney CID via 101 or Crimestoppers anonymously on 0800 555 111 or at crimestoppers-uk.org.