New South Wales police are collecting DNA samples from thousands of criminals with spent convictions to help solve cold cases and future crimes.
Police are planning to take a further 2,000 samples over the next 12 months, adding to 1,000 already collected, to build a comprehensive DNA database.
Civil liberties advocates have criticised the program for casting too wide a net and taking samples from people who were, in many cases, rehabilitated.
David Porter from the Redfern Legal Centre, a state-wide service, said there had been a dramatic increase in the use of the practice throughout the year and public resources were being wasted.
"These are people who aren't under suspicion of any crime," he said.
"The police are taking the time to seek their DNA, we are taking our time to advise them in relation to it, the police are taking further time to lodge an application with the local court, the local court is taking time to hear that application.
"I'm not sure what evil it is addressing."
Officers have had the power to request DNA samples from past offenders for seven years, but the practice has been relatively rare until recently, when it was made a priority.
Under the program police can visit the homes of past offenders to request a DNA sample if they meet specific criteria.
The offenders must have served prison time for a crime that has a maximum sentence of more than five years and have been charged with a further offence, although not necessarily convicted.
Former offenders receive a letter stating that if they decline to provide a sample a court order will be obtained to compel them to.
NSW Police Assistant Commissioner Peter Cotter said the database would help police solve old and new crimes.
"Across the whole spectrum of crime types from minor property type crimes where no-one has been hurt all the way through to the real serious types of crimes such as serious assaults, sexual assaults," Assistant Commissioner Cotter said.
He said the program focused on past offenders who had a "fair chance" of becoming repeat offenders.
But solicitor David Porter said the program was catching people who, in some cases, had only spent days in prison.
"Generally speaking, I think most members of the public would agree that we don't need to be performing DNA tests on serial shoplifters," he said.
NSW Greens MP David Shoebridge said the program was an attack on civil liberties.
"At a minimum, we should be having the Ombudsman overseeing this process," Mr Shoebridge said.
"This has been a very secretive operation by the New South Wales Police that we've only really obtained evidence from anecdotally and that is not good enough when you're talking such a substantial use of police resources and such a significant attack on civil liberties."