The detective who led the Shannon Matthews investigation said the schoolgirl was lucky to be found alive.
For 24 days, the nine-year-old was kept captive in Michael Donovan's flat as part of a plot by him and her mother Karen Matthews to claim £50,000 in reward money.
Traces of temazepam in the youngster's hair indicated prolonged use of the sedative drug which Det Supt Andy Brennan said could have been fatal.
"It beggars belief that a mother would put her own child in this position," said Mr Brennan.
"She'd [Karen Matthews] have had no idea when Shannon was being administered these drugs as to what effects they had on her."
Mr Brennan said he doubted whether the body would have been recovered if the girl had died.
"Donovan I'm sure would have disposed of the body and I don't think Karen would have helped us.
"We look at the role Donovan and Matthews played in this, they are solely responsible for her disappearance, they are solely responsible for her being held hostage and captive at Donovan's flat and also the administration of the drugs she's received. She's lucky to be alive."
During the huge police search - one of the most expensive and highest-profile missing person inquiries seen in the UK - Karen made tearful pleas for the safe return of her daughter.
And as the investigation intensified, Mr Brennan said his hopes of finding Shannon alive started to fade.
Mr Brennan said: "Anyone who hears the 999 tape on the Tuesday evening that Shannon is reported missing would have no doubt at all that that is a mother who is clearly saying her daughter is missing.
"She's very concerned and that's how she continued during the three-and-a-half weeks until we rescued her from Donovan's flat."
But the detective said police were beginning to pick up on inconsistencies in Karen's version of events.
On 14 March, the youngster was found hidden in the base of a divan bed at Michael Donovan's flat in Lidgate Gardens, Batley Carr.
When Mr Brennan was told the news over the phone, he said his initial response was a presumption Shannon had been found dead.
"Three-and-a-half weeks into the inquiry I just took it as an assumption that we had found the body somewhere and we would go into our normal homicide investigation process."
He added: "[When] I was told, 'No she's alive', it really stopped me in my tracks.
"A short while later I arrived back at Dewsbury Police Station and I went to the room where Shannon was... they [detectives] introduced Shannon to me and told her who I was, she said hello and smiled, I said hello and smiled. Nothing more needed to be said at that time and it was just she's there, she's alive.
"One of the officers said to me you can't buy moments like that and you can't."
Despite being found guilty of charges of kidnap, false imprisonment and perverting the course of justice, Mr Brennan believes Karen Matthews will never reveal why she did what she did.
"She's given a version of events and I don't think she will ever tell anyone the truth because of the seriousness of what's happened."
He added: "Karen's interest and motivation throughout all this has not been for Shannon or anyone else, it's been for her and getting her hands on £50,000.
"Michael Donovan is a sad, pathetic individual...but behind that is someone who clearly knows what they're doing.
"He's trying to put himself over as the victim in his own right and that's outrageous."