On Monday the Parole Board said the 61-year-old was suitable for release.
Dawn's uncle Philip Musson said the family had lived "in fear" of the decision, adding "there is no parole for Dawn or Lynda".
Pitchfork was the first murderer convicted on DNA evidence, after raping and killing the two 15-year-olds in the 1980s.
He was last denied parole in 2018.
Now the Parole Board has authorised his release after the panel heard Pitchfork's "behaviour in custody had been positive and had included extensive efforts to help others".
The announcement
has been sharply criticised by the victim's relatives and some politicians.
A source close to Justice Secretary Robert Buckland said the government would take legal advice to explore the use of a "reconsideration mechanism" to halt Pitchfork's release.
The
Parole Board Reconsideration Mechanism, introduced in 2019, gives people 21 days to ask for a decision to be looked at again if they believe it was "procedurally unfair" or "irrational".
But Gavin Dingwall, Professor of Criminal Justice Policy at De Montfort University, said this would not be straightforward.
"So there is an appeal mechanism of sorts but Mr Buckland can't appeal just on the basis he felt uncomfortable with the decision, the Parole Board has the status of a court," he said.
"It is always going to be very difficult for a politician to challenge the decision of the Parole Board.
"They would have to prove the board did not follow correct procedure, for example did not consider key evidence.
"The other grounds - irrationality - would basically be a very, very high standard. [It would need] decision-making which was counter to any form of logic."
- Colin Pitchfork, 22 at the time of the first murder, was married with two sons. He was a baker who grew up in rural Leicestershire and lived in Littlethorpe
- In November 1983 he left his baby son sleeping in the back of his car and raped and strangled 15-year-old Lynda Mann in Narborough. He then drove home and put his son to bed
- Three years later, less than a mile from where Lynda died, he raped and murdered Dawn Ashworth, also 15, of Enderby. The pathologist who examined her body described it as a "brutal sexual assault"
- A police investigation initially led to the wrong man, a local 17-year-old who falsely confessed to one of the killings. After an unprecedented mass screening of 5,000 men using pioneering "DNA profiling" technology, Pitchfork was eventually caught. At first, Pitchfork had evaded justice by persuading a colleague to take the test for him
- He pleaded guilty to both murders in September 1987 and was sentenced to life in January 1988. The judge said the killings were "particularly sadistic" and he doubted Pitchfork would ever be released
if he doesn’t get the parole revoked 
