Bidhya Sagar Das, 33, lived at the address in Finsbury Park area in north London where the toddlers were attacked in what police are describing as a suspected “domestic incident”.
“Detectives are urgently trying to trace a man who was at the flat shortly before the injured children were found, but left before emergency services were called. The man has not been seen since this time,” the Metropolitan Police.
Horrified neighbors had reported a woman, believed to be the children’s mother, rushing out of the home screaming, “My children, my children!”
The boy was pronounced dead after both the children were taken to an east London hospital.
The little girl remains in a critical condition in hospital.
Officers were seen going door-to-door as police remained outside the three-storey building. Neighbours said officers had been searching properties along the tree-lined street.
The Metropolitan Police have not confirmed how the children were injured, but said a murder investigation has been launched by its Homicide and Major Crime Command.