"Groundbreaking": Police are DNA testing its newest crop of student police to screen them against its crime database. Photo: Phil Carrick

For the first time, the NSW Police Force has used DNA testing to screen its newest crop of 189 student police against its crime database.

The screening at the police academy last Saturday coincided with new figures, obtained under freedom of information laws, that showed 437 active police in NSW have 595 criminal convictions.

About 70 per cent of those convictions, including break, enter and steal, and serious drink driving convictions, were committed before officers were employed by the police. Another five convictions were recorded by student police, including two fraud charges, and another six were by probationary constables.

The DNA testing, using swabs from inside the mouth, was ''groundbreaking'', assistant commissioner Michael Corboy said in a statement. ''It is a further layer of comfort to us that we are hiring the right people.''

Mr Corboy, commander of education and training, stressed the testing had been ''long scheduled for that day,'' and that the decision to introduce DNA testing was made by Commissioner Andrew Scipione's executive team last November.

In addition to DNA tests, every aspiring police officer will also face a face-to-face behavioural interview by a panel.

The results of the DNA testing are not yet available, but Greens MLC David Shoebridge said it would detect only those who did not already have a conviction.

And it did not answer the question as to why there were so many police with convictions.

''It beggars belief that an individual can be convicted of a serious fraud while a student police officer and still be assessed as a constable in NSW,'' Mr Shoebridge said.

Mr Scipione has said that many of the pre-employment offences can be traced back ''four decades, back to the 1970s''. But his office said some matters related to when these serving officers were children as well as spent convictions. In other words, a conviction that is no longer a criminal record.

There had also been an overhaul of recruitment in 2009 to ''exclude the vast majority of applicants with criminal convictions''. The changes also restricted entrance by candidates with drink-driving convictions, banning anyone with a mid-range offence in the past five years, and anyone with a high range in the past 10 years.

Police in Tasmania, South Australia and Western Australia use DNA testing. The NSW force says it will use DNA testing only for matching purposes and will destroy the sample afterwards.

President of the NSW Council for Civil Liberties Stephen Blanks said it was curious the Police Association had in the past advocated the use of DNA testing on suspects, even witnesses, but opposed its use for police. If the purpose of the testing was to identify a criminal conviction, DNA was not necessary, he said. He said there were also real risks that a police officer's DNA could be mixed with a suspect. ''I really query whether it is necessary,'' he said.