DNA has been a key feature both in convicting Steve Wright for the murders of five women in Suffolk and in the Sally Anne Bowman case.
DNA is playing an increasingly important role in fighting crime
At present, the DNA profile of everyone arrested for a recordable criminal offence is added to the national database.
The DNA database, which covers England and Wales, contains around 4.5 million profiles. Steve Wright's was amongst them.
He had been convicted of theft in 2003.
When police found his DNA on the bodies of some of his victims they were able to match it with his profile on the system.
In the Sally Anne Bowman case, Mark Dixie was not on the system at the time of the murder. Although he had a criminal record, his convictions took place before the database came in.
Then in June 2006, he was arrested for assault after a fight in a bar. Police took his DNA and the link with Sally Anne Bowman was made. He was arrested within five hours.
The case has prompted calls for a universal database containing everyone's DNA.
Det Supt Stuart Cundy, who headed the murder investigation, said it was not the first time such calls had been made.
"It is my opinion that a national DNA register - with all its appropriate safeguards - could have identified Sally Anne's murderer within 24 hours.
"Instead it took nearly nine months before Mark Dixie was identified and almost two and a half years for justice to be done."
The Association of Chief Police Officers (Acpo) has added its voice to calls for a debate on the database issue.
The Chief Constable of Lincolnshire, Tony Lake, speaks for the association on DNA.
He said: "If there was a national database of everybody then we would solve more crime, of that there is absolutely no doubt.
"In the conviction of Steve Wright - and today of Mark Dixie - you've heard about the vital importance that DNA played. But any database that we hold has to be reasonable and proportionate in the eyes of the public."
The Home Office said the government position over a universal database remained unchanged: there were no plans to introduce one.