A hidden weapon is helping police fight crime - even though it's completely invisible!

Police in Maidstone have a new scanning system in their custody suite, which scans arrested people for traces of something called smart water.

Smart water is a forensic marking which covers offenders or property with a harmless solution, which is invisible to the naked eye but is detectable under ultra violet lights (UV).

If the offender or property glows under the lights, a swab will be taken of the substance and the unique code directly linked back to a specific crime scene or location.

It can also be used as a property marking system, giving a greater chance of returning stolen items to their rightful owner.

Detective Chief Inspector Nick Gossett of Maidstone police said: "Criminals need to be aware that forensic marking has a 100 per cent conviction rate to date with an irrefutable link to the scene of a crime.

"Already where similar trials of the substance are being used they are having excellent results, with noticeable reductions in burglary, robbery and theft."

The solution remains on skin and hair for weeks and on clothing indefinitely, no matter how hard offenders try to scrub it off.