"The retailer was on the verge of tears," Mr Cleary recalled of the event 12 years ago. "He'd done everything the insurance company had asked - alarm, grilles at the windows and £10,000- worth of closed-circuit television. But the burglars chipped out the mortar round the window shutters and covered their faces with football scarves. The alarm worked perfectly, but they were in and out within three minutes."
Here, he felt, was first-hand evidence that the £2.5bn Britain spent annually on electronic security was no guarantee of deterrence or capture. Worse was to come. Thanks to a tip-off, Detective-Constable Cleary traced one of the shop's missing camcorders to the home of a 15-year-old youth. He had him bang to rights. There was, though, just one problem. Without a serial number, the retailer would have been unable to convince a court that this particular camcorder was stolen from his shop. Exit a sneering 15-year-old (camcorder under arm) to a hero's welcome from his mates.
"What we wanted in cases like this," Mr Cleary said, "was some irrefutable evidence. The one thing the criminal does fear is forensic science because he knows the court will convict on it. But the forensic boys always come in after the offence has been committed. I wanted to produce something that would act as a deterrent."
He had long discussions with his brother Mike, an industrial chemist. What he wanted was a canister that could be activated by an electronic impulse to spray an intruder with a safe, water-based substance that would show up only under an ultraviolet lamp. To satisfy a court, it would have to have the capacity to be tailored individually to each building where it was installed.
The result was Index Solutions, which has impressed the Home Office enough for it to classify the Cleary product as an invention of national importance and buy the manufacturing licence.
Index is distributed by the Cleary brothers from their company, Probe FX, at Walsall in the West Midlands. More than 80 systems have been sold. Customers include BP, Asda and the Salford education authority.
Plans are afoot to set up a distribution network in mainland Europe, with backing from the investment company 3i. The entrepreneurial instincts of Mr Cleary are beginning to pay off.
He left the police in 1990 and started his own security company. First Watch now has a staff of 40 and a turnover of £500,000.
Trials of Index have taken place in Stoke-on-Trent, Bristol and Newcastle, where word quickly spread among criminals. One electrical store that was burgled 15 times in nine weeks during 1992 has remained untouched for three years. Probe FX has taken out extensive patents. Stealing a policeman's invention could be a serious offence.