FOGGIA -- A French woman tourist who spotted a mafia assassination team while on holiday in Apulia has emerged as a key witness in the hunt for gunmen who shot and killed four people as police arrested a crew of four heavily armed mobsters evidently poised to carry out another deadly ambush in the southern Italian region, police said.

 The woman, who has not been identified, was driving in the Gargano region last Wednesday when she came across four masked men speeding in the opposite direction carrying assault rifles, Carabinieri paramilitary police sources said. A short time later she encountered a patrol of local municipal police and tried to raise the alarm but failed to make herself understood because of the language barrier.

 The tourist persisted and went to the nearest Carabinieri barracks though police have denied reports she has been given a police escort. "She is not under protection," a Carabinieri source said, "she presented herself spontaneously at the barracks to explain what she had seen, after learning there had been a quadruple murder" in the village of San Marco in Lamis.

Apulia, with its long coastline, sandy beaches and excellent wines, is a favorite tourist destination for Italians and foreigners. The rugged Gargano promontory offers panoramic views and picturesque seaport towns surrounded by crystalline waters.

 On Saturday Carabinieri officers in the town of Torremaggiore, known to be used as a logistics centre for the Sacra Corona Unita, the little-known Apulian mafia, arrested four mobsters described as "armed to the teeth" as they emerged from a garage in a car and on a powerful scooter. Officers seized loaded pistols  and a machine pistol as well as full facial crash helmets.

"We are absolutely convinced we have prevented another murder being carried out," said Col. Marco Aquilio, the the Torremaggiore Carabinieri commanding officer.

 Suspects for the quadruple slaying are being sought in the Li Bergolis underworld clan, traditional enemies of Mario Luciano Romito, the mob boss who was gunned down with his brother in law and two passers-by who witnessed the ambush.

All four men arrested had criminal records. "They were ready to open fire, with rounds in their gun chambers .. armed to the teeth."

 "We are certain that Torremaggiore is used as a logistic base by criminals. We don't know who the designated target was," the colonel added.

 One of the four arrested men was identified as Tommaso D'Angelo,  considered close to the Moretti-Pellegrino-Lanza clan active in the provincial capital of Foggia.

 Police sources said there was no obvious link between the latest arrests and the Li Bergolis clan suspected of the ruthless slaying of Romito. Two members of the Li Bergolis clan with criminal records are sought by police on suspicion of involvement in the quadruple murder but have disappeared, the sources said