The police failure to find Tia Sharp's body more quickly, was not down to an individual officer, the Metropolitan Police Commissioner has said.
Officers investigating the disappearance of the schoolgirl, searched the New Addington home of her grandmother four times, before her body was eventually found in the loft on August 10.
The Met Police has apologised to the 12-year-olds mother Natalie Sharp for the delay in finding her body.
Met Commissioner Bernard Hogan-Howe said: "If we thought it was an individual human error then that would explain it, but we are carrying out a review because we are not happy that explains it.
"We are trying not to have a knee-jerk reaction, we need some time to understand what happened and what failed to happen.
"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."
Mr Hogan-Howe said he hopes the internal review will provide answers about what happened in the coming weeks.
He added: "We have explained it was human error but we want to go into it more. You can always blame the individual but we want to understand the processes and management decisions we have made that led to the failure.
"In a few weeks' time we will have some conclusions so that we make sure it doesn't happen again."
Stuart Hazell the partner of Tia's grandmother, has been charged with her murder. The 37-year-old is due to appear at the Old Bailey on November 19.