The failure to find 12-year-old Tia Sharp's body more quickly was not down to an individual officer, the Metropolitan Police Commissioner has said.
Tia's grandmother's terraced house in New Addington, south London, was searched four times by police teams before her body was finally found in the loft.
It is understood that the body was wrapped in bin bags when it was discovered.
Police didn't find the body of Tia Sharp despite searching the house in New Addington four times
The force has apologised to Tia's mother Natalie Sharp for the delay in finding her and put it down to "human error". A review is being carried out into the delay.
Bernard Hogan-Howe said: "If we thought it was an individual human error then that would explain it, but we're carrying out a review because we're not happy that explains it.
"We're trying not to have a knee-jerk reaction, we need some time to understand what happened and what failed to happen.
Stuart Hazell, Tia's step-grandfather, was arrested after her body was found
"We want to learn lessons from this particular case. We have apologised and I repeat that apology today to Tia's mum and family for not having found Tia's body sooner."
He said he hopes to have some answers within "a few weeks" after an internal review was carried out.
"We've explained that it was human error but we want to go into it more. You can always blame the individual but we want to understand what processes and management decisions we've made that led to that failure.
"That's why we're carrying out a review and we hope in a few weeks' time we will have some conclusions from that, so that we make sure it doesn't happen again."
Tia's grandmother's partner Stuart Hazell, 37, from New Addington, has been charged with her murder and is due to appear at the Old Bailey for a plea and case management hearing on November 19.