Det Ch Insp Alison Foxwell said on Saturday: “At this stage, we believe the incident occurred within a domestic context, but we are appealing for anybody with information to come forward.”
She added: “The death of an infant is always an extremely tragic occurrence, and officers are making urgent enquiries around the circumstances.”
A guarded police cordon was set up on Great Peter Street, just off Horseferry Road, following the incident, and forensics officers also attended the scene.
Tributes were placed near the scene on Sunday, including flowers and a toy animal, after the cordon was lifted.
Detectives from the Met’s Specialist Crime Command are leading the murder investigation.