It was a mystery that had police puzzled for a while: a rash of thefts reported by passengers who had taken the 75-minute bus trip between Paris and Beauvais airport.

An eagle-eyed driver has been credited with helping crack the case last week after he spotted a suspicious suitcase being loaded onto his bus as he prepared to drive from Paris to the airport, a hub for low-cost airlines.

Acting on his tip-off about a large brown bag that appeared to be moving on its own, police at Beauvais pounced on a Romanian man who picked up the suitcase and a smaller black rucksack as he arrived.

After arresting him, detectives found an accomplice hidden inside the case who, once alone in the baggage hold during the trip, would pull a strap to unzip himself and then begin his thieving.

"In the black bag we found two laptops, money and various objects of value," a police source told AFP on condition of anonymity.

Both men, aged around 40, were from Romania and had criminal records for theft.

The man inside the suitcase received an eight-month prison sentence on Monday when he appeared in court, while the other man was given a one-year prison sentence because of his more serious criminal record, prosecutor Florent Boura said.