Yorkshire & Lincolnshire

Last year in the UK around 5 million crimes were reported to the police.

Of these a staggering three-quarters of victims never see justice done.

From manslaughter to murder, robbery to rape - imagine how many cases that leaves unsolved over the past 30 years.

But science is now catching up with cold cases as detectives go back to dusty files and local libraries to retrieve the evidence that is increasingly putting murderers and rapists behind bars decades after they committed their crimes.

'Life on Mars' in reverse

The South Yorkshire Police cold case review team is led by Detective Sergeant Ian Harding, and includes three retired detectives who sometimes end up working on cases they remember from the first time round. 

Retired detective Ray Hooley describes his job as "like Life on Mars in reverse".

The detectives work with scientists from the Forensic Science Service in Wetherby near Leeds.

Det Serg Ian Harding - never gives up on a case.

They use the latest advances in DNA technology to try to catch the criminals.

Fortunately, many of the original samples from crimes going back even as far as the 1950s are still kept at a secret location.

The scientists are now able to re-test these samples and check the DNA database to see if they can find a match.

Once a match is found, the team re-investigate the crime.

They sometimes piece together evidence using old police files but often these have been destroyed so they have to rely on local newspaper archives and libraries for information on the original crime.

Tracking down witnesses

Witnesses who could have moved anywhere in the country and sometimes even abroad then have to be tracked down.

Family liaison officers have the delicate task of re-approaching victims to ask them to testify.

PC Jill Thomas - persuades victims to testify.

It can make the difference between bringing a case to trial and getting a conviction - and the case going cold again.

BBC Inside Out has been given exclusive access to the cold case squad as they track down rapists and murderers long after they thought they’d got away with it.