They were daredevil highwaymen whose meticulously planned motorway heists combined precision driving with death-defying acrobatics.

On Friday Spanish police made a series of arrests in and around Madrid detaining 23 members of a gang who they say specialized in robbing moving trucks without the drivers noticing.

The Civil Guard believe the the gang crisscrossed the country and pulled off more than 50 thefts from trucks in a two-year crime spree that brought them millions of dollars.

With little apparent thought for their safety the thieves often targeted trucks at night on quiet stretches of motorway.

The gang used a car to overtake and then pull in front of a lorry, forcing it to slow down. Other gang members in following pick-up trucks would then draw up behind the truck. A daring robber would walk down the bonnet of the pick-up and leap from it and on to the back of the moving truck.

Using a rope or a suction cup device to hang on, the thief then used either a battery-powered grinder or a crowbar to pry open the truck's rear doors.

Other members of the gang clambered across the bonnet of the pick-up truck and jumped into the back of the big rig.

They then passed back the loot, which was often computers, mobile phones, brand-name clothes, sunglasses or perfumes.

The stolen goods were immediately packed into waiting boxes in the back of the pick-up truck, ready to be sold on.

Once the thieves were satisfied, or the lorry emptied, the gang sped off. Sometimes several pick-ups would be filled from the back of a single moving truck.

The goods were sold immediately to waiting buyers. The gang, made up of Romanians and Spaniards, carried out raids to order and always targeted trucks they knew would carry highly valuable loads, sometimes using tip-offs from criminal contacts within freight companies.

On other occasions police believe that the gang followed trucks that they intended to rob from industrial estates where they had watched them being loaded up with high-value goods.

Police believe that they can link the gang to at least eight high-speed heists in Toledo, Cuenca, Ciudad Real, Albacete, Madrid, Valencia, Cordoba and Granada. The driver of the trucks were usually unaware that the vehicle was being robbed.

In a dragnet operation carried out this week, Civil Guard officers arrested 20 Romanians and three Spaniards. Detectives also carried out raids at 10 addresses in Madrid and the nearby town of Coslada.

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