Police in Alsace at first suspected the IRA of trying to steal a vehicle in France for an operation against a British base in Germany. The next day, Mr Schwanger, the chief executive of Josy Tourisme which operates the Checklines coach service from Strasbourg, found his car tyres had been punctured.
Ten days later, a grenade exploded under another minibus. At the end of April, 400 litres of petrol in Mr Schwanger's garage were set alight by a Molotov cocktail, destroying two coaches. On 5 May, a minibus was sprayed with automatic fire as it negotiated a roundabout. The driver and a passenger were injured. Four days after that, another burst of fire hit the offices of Josy Tourisme.
The attacks were an aggressive competition policy put into practice by a German rival, Airportlines, in Baden-Wurttemberg.
On 11 May, Rudolph Schropfer, the husband of the owner of Airportlines, was arrested in a red Volkswagen Passat parked along the route of a Checklines bus. German police found an automatic pistol, grenades and two magazines of ammunition. Another Airportlines employee was arrested later.
The rivalry revolved around a lucrative trade in bussing airline passengers from eastern France to German or Swiss airports. The original services were operated by German firms between the Alsatian capital and Frankfurt.
A year ago, however, a group of businessmen in Alsace invested in Josy Tourisme to create Checklines, a luxury minibus service, which at 550 francs (pounds 65) a passenger, was 20 per cent more expensive than the established competitors.
The upmarket Checklines - hot and cold drinks, airline seats and newspapers in three languages - appealed to the airlines. Lufthansa soon gave 60 per cent of its orders to the Alsatian firm. It is currently conducting negotiations for a contract under which Checklines would be its exclusive transporter.
It was, a shocked Mr Schwanger said, 'commercial terrorism' which should never have gone beyond 'punctured tyres or sugar in the fuel tanks'.Reuse content