The Director of Public Prosecutions personally led the moves to quash Gary Allen's acquittal for the killing of Samantha Class after describing him as "evil".
Max Hill QC said he was so concerned about the murder of Ms Class that he presented the case for a retrial of Allen to the Court of Appeal himself.
And Mr Hill has rejected suggestions that this application could have been made earlier before Allen killed Alena Grlakova in 2018.
Mr Hill said: "In Allen, we have an individual who is exceptionally devious in his attitude towards the crimes that he committed.
"Frankly it's hard to find any other word for him than evil."
Mr Hill said: "I'm delighted that justice has been delivered for the family of Samantha Class as well as the family of Alena Grlakova."
He said: "When we were presented by the police with a combination of the new and compelling evidence, we realised that we had enough to make an exceptional application to the Court of Appeal under the new law.
"I was so interested and concerned in this case that I decided to go to the Court of Appeal myself and presented the case to the judges personally."
Mr Hill added: "I need to emphasise that it's not in every case that we're able to go to the Court of Appeal. The test that the law now sets is a very high one. In almost every case the law means that, once a jury has pronounced a not guilty verdict, there can never be a second chance."
Gary Allen was cleared of murdering Ms Class by a jury in 2000 and his retrial was only possible when the Criminal Justice Act 2003 ended the age-old bar against double jeopardy, which held that no one could be tried again for the same crime.
But the law change set a high bar for any double jeopardy application, saying there had to be "compelling new evidence".
There were four new strands of evidence that were presented to the Court of Appeal to overturn the double jeopardy rule.
The first were Allen's attacks on two women in Plymouth within weeks of his acquittal. The second was concerning comments he made to probation officers after he was jailed for these attacks.
The third was the confessions he made to an undercover police officer in 2010 and 2011. And the fourth was the similar murder of Ms Grlakova.