Tokyo police suspect that three people involved in a robbery this week at a luxury watch shop in the Ginza shopping district had been assigned different roles to play in the heist.

Three masked people forced their way into the shop on early Monday evening and left with merchandise in a car.

Investigative sources say the robbers committed the crime in two minutes.

As soon as they entered the shop, one of the three threatened staff with a knife while the other two started smashing showcases with crowbars and taking out watches. The first person later joined in.

Before leaving the store, one of the three told the others that they could continue stealing for at least 30 more seconds.

Later that night, police arrested four males aged 16 to 19 in Tokyo's Akasaka district, near Ginza. They are suspected of trespassing at a condominium close to where police found the vehicle used in the robbery.

The police say about 70 watches worth 250 million yen, or about 1.9 million dollars, were stolen, and that all of them were found in the car and near the condominium.