Holly Wells' father says he will be waiting for Ian Huntley if the Soham murderer is released from jail.
Holly Wells' parents have vowed to try to get on with their lives
Kevin Wells vowed to be there even if it was 50 years before Huntley - jailed for life for killing Holly and her friend Jessica Chapman - was freed.
And Holly's mother, Nicola, told ITV1's Our Daughter Holly - a Tonight Special she wanted to "hang him very slowly".
However, the couple also speak of their determination to get on with their lives for the sake of their son Oliver.
Mrs Wells said: "Obviously a major part of my life has been taken away, but we need to carry on and try to be as normal as possible for Oliver.
"He has got us through it. He has tried not to show too much emotion. We have tried to keep his life as normal as possible."
The 90-minute documentary - which is being shown without adverts - sees Holly's parents, family and friends talk about the girl with a "lovely nature" who loved Britney Spears and Kylie Minogue.
Mr Wells describes how he penned a "goodbye letter" to his daughter, which he took to the mortuary.
He said: "It was a goodbye letter, a sorrowful letter. There was an element of apology in the letter as well."
Asked what could have been done differently, Mr Wells said: "At that time, there were many unanswered questions.
"We didn't know what had happened to Holly. We had a suspect but no details.
"Was there something as a parent that could have been done? Something that could have taught Holly, that should have been mentioned to Holly that could
have made her more aware of her position? That was the area of apology."
He also tells of how he had repeated visions of Holly in an empty bath long before Huntley's trial.
During the trial last year, Huntley said that Holly had drowned in his bath when he accidentally killed Jessica by covering her mouth to stop her from screaming.
Huntley, 29, is serving life in jail
However, the Old Bailey jury convicted Huntley of the 2001 murders in Soham, Cambridgeshire, and the former school caretaker was jailed for life.
Mr Wells said: "50 years now appears to be the minimum sentence that Ian Huntley is going to serve.
"That makes me 90 when he will be released - if he makes it through that period of his life. When I said I would be around to go and meet him, I meant it," he said.
Of Huntley's former girlfriend Maxine Carr, who was jailed for conspiring to pervert the course of justice, Mrs Wells said: "I think she's got a life sentence now anyhow."
Our Daughter Holly - a Tonight Special will be screened on ITV1 from 9pm on Thursday, March 11, 2004.