PARIS – Somewhere in the world, there’s a navy blue suitcase with a small pack of explosives tucked in its side pocket.

Four days after police at Charles de Gaulle Airport slipped some plastic explosives into a random passenger’s bag as part of an exercise for bomb-sniffing dogs, it is still missing, and authorities are stumped and embarrassed.

Police have sought to minimize public concern by insisting there’s nothing to worry about: the explosives had no detonator and are unlikely to pose a danger.

“I picture myself opening my bag at home,” said Chadi Kawkabani, an American tourist on his way to the airport Tuesday. “You might think terrorists planted the explosive – and they could come to your house to get it back!”

Authorities believe the suitcase left Paris between 5 and 7 p.m. Friday and could have wound up on any of about 100 flights.

“There were flights that went to the United States, to Japan, South America,” police spokesman Pierre Bouquin said. “Basically, it could have gone anywhere – to the four corners of the world.”

Authorities at airports in New York and Los Angeles launched a fruitless search for the suitcase.

The training exercise was aimed at providing sniffer dogs a real-life airport scenario, a technique that has been used for years, Bouquin said.

Two police officers involved in the exercise stashed a cellphone-sized pack of plastic explosives into the side pocket of the navy blue suitcase as it rolled along a conveyer belt. One dog successfully identified the bag, but police then lost track of it when they went to fetch a second dog for the exercise.

Police quickly ordered a halt to using real luggage for practice.

As for lost bags, they tend to turn up “pretty quickly,” generally within a week, said Corinne Bokobza, spokeswoman for Aeroports de Paris.

But that’s when the bag is ticketed and traceable through the computer system. Finding a navy blue suitcase lost somewhere in the world, she said, “could take a while.”