Police have set up a computer system which will allow UK forces to share intelligence on 15 million people.
A Police National Database was the key recommendation from the Bichard Inquiry into failings by police into the Soham murders in 2002.
It found that police failed to disclose details of allegations against Ian Huntley a year before he murdered Holly Wells and Jessica Chapman, both 10.
Privacy campaigners say non-criminals should not be on the system.
The database, which brings together 150 separate computer systems, combines intelligence from the 43 police forces in England and Wales.
It also links to the eight police forces in Scotland, the British Transport Police, the Police Service of Northern Ireland, the Child Exploitation and Online Protection centre (Ceop), the Serious and Organised Crime Agency (Soca) and the military police.
Collectively the forces hold information on between 10-15m people. These include convicted criminals, suspects and victims of crimes, as well as the details of people who have been questioned by police but not charged.
The database is run by the National Policing Improvement Agency (NPIA).
The Bichard inquiry said police should be able automatically to access information on suspects held by another force.
Holly's father, Kevin Wells, said the launch of the system was a "defining moment" that would make it harder for criminals to use police force borders as a shield to avoid detection.
He said the database was "the perfect end-product befitting such a high-profile inquiry".
In a letter to NPIA, Mr Wells wrote: "In much the same way as we've privately shared our positive feelings and views to you and the team, there does exist a desire to shout about this achievement and herald its successful arrival to a wider audience.
"It would after all be an appropriate reaction from two parents witnessing a defining moment to mark the passing of their daughter."
He said it could make the 10th anniversary of Holly's death next year "so much easier to bear".
Sharon and Les Chapman, parents of Jessica, said: "We hope [the database's] use will mean other families don't suffer the same loss and heartbreak as we did."
Lord Bichard, who first recommended a national database in 2004, responded to concerns about a single database holding so much information by saying it was a question of "balancing the risk of someone hacking into the system with the risk of another Huntley".
His inquiry had found that Humberside and Cambridge police forces failed to properly vet Huntley, a school caretaker who had been accused of several sex-related crimes.
There were eight separate pieces of intelligence on Huntley but they were not brought together because they were held by separate police forces.
NPIA chief executive Nick Gargan said: "Many people will be surprised to know that the police service has not had this capability for many years. The good news is that they have it now."
Privacy campaign group Big Brother Watch said it was concerned that details of members of the public could be logged on the database.
Spokesman Daniel Hamilton said: "Nobody has a problem with a database of criminals but we should never build a database of innocent people and crime victims.
"The risk of this data falling into the hands of criminals is too horrifying to comprehend."