By Mona McAlinden
BBC Scotland news website
In Scotland, most DNA is destroyed if there is no charge or conviction
For more than two years, Scottish police forces have been able to retain the DNA of anyone arrested but not convicted of a sexual or violent offence for an initial three-year period.
If chief constables have intelligence that the individual poses a potential risk of offending, they can apply to a sheriff to have the DNA retained for a further two years.
But DNA samples from people arrested but not convicted of any other offences are routinely destroyed in Scotland, a situation which contrasts with other parts of the UK.
When the DNA database was launched south of the border in 1995, the only details that could be stored belonged to convicted criminals. But the law changed in 2004.
From 2004, the DNA profiles of everyone arrested for a recordable offence in England, Wales and Northern Ireland were kept on the database, regardless of whether they were charged or convicted.
At present there are about 4.5m profiles on record.
But in 2008 the European Court of Human Rights ruled the UK database - apart from in Scotland - was illegal.
The court said that holding the profiles of innocent people "could not be regarded as necessary in a democratic society".
It ruled this level of retention was "blanket and indiscriminate".
In response, the Home Office said DNA profiles of up to 850,000 innocent people would be removed from the database.
But details of those cleared of crimes - or never charged - will still be held for six years, or 12 in cases of serious violent or sexual offences.
The European Court considered the system in Scotland "fair and proportionate".
The Scottish model was developed following a review by Professor Jim Fraser, director of the Strathclyde University's Centre for Forensic Science.
Following the Home Office announcement, he said the central question was whether holding samples for 12 years was "proportionate".
"When I addressed the issue in Scotland it was very difficult to come to a firm conclusion that three years was the period," he said.
"What I concluded was that it was a reasonable period because most offenders - if they are offenders, and if they do re-offend - will probably offend within a two or three-year period and that was on the basis of data which was specific to Scotland."
He called for a similar examination to take place in other parts of the UK to look at the issue of proportionality.
"I would like to see the evidence to justify the 12-year period," he added.
The Scottish Government said it had proposed more changes to the law "to strengthen the regime further".
This includes introducing the temporary retention of forensic data from children who have committed serious violent or sexual offences and are dealt with through the Children's Hearings system.
The government spokesman added: "Clearly any legislative changes must be properly balanced to ensure they safeguard the rights of individual citizens, while also providing police with effective and proportionate powers to further protect our communities."