This is the first picture of a one-year-old boy killed in an attack in a Finsbury Park flat which also left his twin sister critically injured.
The picture emerged as police revealed they had arrested 33-year-old Bidhya Sagar Das, who is understood to be their father.
The children, named locally as Gabriel and Maria, were rushed to hospital after the incident but the boy died just before 1am on Sunday.
The girl remains in hospital in a critical condition.
Das, who lives at the apartment in Wilberforce Road where they were found, was arrested in the Hackney area on suspicion of murder and attempted murder on Sunday evening.
A hammer reportedly found dumped in a bag of sand near the apartment is being examined by forensics officers, although the Met would not comment on its relevance in the investigation.
Scotland Yard said officers were alerted to the incident at 11.10pm on Saturday.
Police said Das left the flat shortly before the emergency services were called.
Neighbours said a woman was heard frantically shouting for help before scores of police arrived at the scene.
This is believed to be the twin’s mother, named locally as Cristinela Datcu.
A woman living opposite the building, who gave her name as Gui Gui, said: "I was watching TV. I heard someone was shouting. She kept on shouting. I do not know what she was shouting.
"I opened the window and I asked her 'Can I help you, can I call the police for you?' She said, 'My kids'."
Medics rushed the injured children, believed to be twins, to the Royal London Hospital.
One child was taken to the hospital by air ambulance and the other by ambulance.
The boy was pronounced dead shortly before 1am in hospital.
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.”
He added the incident is believed to be domestic.
Anyone with information that may assist the investigation is asked to contact the incident room on 020 8345 3775 or Crimestoppers on 0800 555 111.