A cross-Border investigation is under way into a scam where motorists in the Republic have paid up to €4,000 to criminals in Northern Ireland to get their stolen vehicles returned to them.
In all cases the ignition keys had been left in the cars, making insurance cover void.
Since last November at least 20 vehicles, including four-wheel drives, vans and new high-specification cars, have been taken. All were worth at least €12,000. Sources said more vehicles may have been taken but not reported.
The thefts, which began in Co Louth in November, have covered a 60-mile stretch of the Border from Omeath in north Louth to Emyvale in Monaghan.
At least five such thefts were reported to gardaí in Dundalk and another 15 in Monaghan. Eight took place between Monaghan town and Castleblayney.
"These vehicles have been stolen at places like petrol stations when the driver gets out for a few minutes and foolishly leaves the keys in the ignition," a detective said. "One of the gang will then hop in and drive off, it is as simple as that."
The gang searches the vehicle for documentation with the name and address of the owner and then rings them up, demanding large sums, always in cash, before they will hand back the keys.
"People have been asked for anything from €1,000 to €4,000 and in one case, because there was valuable equipment left in it, the owner was quite prepared to pay."
The hand-over is always done north of the Border, outside the jurisdiction of the State.