A post-mortem examination on human remains found at a house in north London was inconclusive, and further tests are under way.
Two women have been arrested on suspicion on murder after the disappearance of a baby more than 11 years ago.
A 50-year-old woman was arrested after officers attended a home on Fryent Crescent in West Hendon on Monday, and a 31-year-old woman was detained in Luton, Bedfordshire.
On Tuesday, detectives re-arrested the two women, as well as a 52-year-old man, on suspicion of preventing a lawful and decent burial.
The older woman has been bailed along with the man until mid-July, while the younger woman remains in police custody.
The investigation into the disappearance of the baby, who was born in Barnet in 2004, was requested by local officers and a child abuse investigation team after a case review into the death of another child at an address in Barnet last year.
A post-mortem examination on the remains at Great Ormond Street Hospital was inconclusive.
A Metropolitan Police spokesman said: "Further tests will be undertaken and this could take a number of weeks.
"We will not speculate on the identity of the child until all further tests have concluded.
"Given the circumstances which led to the launch of this investigation officers from the Directorate of Professional Standards (DPS) have been informed.
"A referral to the Independent Police Complaints Commission (IPCC) has been made.
"Detectives continue to investigate and are liaising with partner agencies."