Officers were called by colleagues in the fire service to an incident in Southchurch Road at about 2.45am on Saturday 3 July, after a property caught fire.
A woman was rescued from the property and was taken to hospital for treatment.
Sadly, a 66-year-old woman has now died.
A thorough examination of the fire site has been carried out by experts and we are now treating the woman’s death as murder.
A 49-year-old man from Southend, who was known to the victim, has been arrested on suspicion of murder and remains in custody this morning.
Anyone who believes they have information on the woman’s death or the hours leading up to the fire should call us on 101 and cite 42/128551/21.