Police were appealing for help to trace Bidhya Sagar Das, 33, (31.12.83) in connection with the investigation. He was arrested in the Hackney area on suspicion of murder and attempted murder at 19:15hrs on Sunday, 19 March.
He has been taken to an east London police station where he remains in custody.
Police were called at around 23:10hrs on Saturday, 18 March, to two children injured at a flat in Wilberforce Road, N4.
Officers attended along with London Ambulance Service (LAS).
The boy and girl - both one-year-old - were taken by ambulance to an east London hospital, where the boy was pronounced dead at 00:48hrs.
Next of kin are aware. Formal identification awaits and a post-mortem examination will be scheduled in due course.
The girl remains in hospital in a critical condition.
A murder investigation has been launched, led by Detective Chief Inspector Dave Whellams of the Homicide and Major Crime Command.
Detective Chief Inspector Dave Whellams, of the Homicide and Major Crime Command, said: "This is clearly a tragic incident, and our thoughts are with the family of the two young children. Despite the best efforts of medical professionals a baby boy sadly died in the early hours of this morning. A baby girl currently remains in a critical condition and is receiving specialist medical care.
"Whilst we remain in the early stages of the investigation, a man has now been arrested. I would still like to hear from anyone who may have any information regarding this terrible incident.”
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