Three British men have been detained over their alleged involvement in a 2015 robbery that netted over ¥100 million ($742,000) worth of jewelry from a luxury shop in central Tokyo, an investigative source said Saturday.

The source said whether the three will be transferred to Japan is being discussed in Britain, which does not have an extradition treaty with Tokyo. They left Japan two days after the heist and were put on an international wanted list by Japanese police through the International Criminal Police Organization, or Interpol.

A Harry Winston shop in the Omotesando Hills commercial complex in Tokyo's Shibuya Ward, where 46 pieces of jewelry worth ¥106 million were stolen, is seen in November 2015. | KYODO
A Harry Winston shop in the Omotesando Hills commercial complex in Tokyo's Shibuya Ward, where 46 pieces of jewelry worth ¥106 million were stolen, is seen in November 2015. | KYODO

The men are suspected of taking 46 pieces of jewelry worth ¥106 million, including rings and pendants, after punching a male security guard and breaking display cases at Harry Winston's shop in the Omotesando Hills commercial complex in Tokyo's Shibuya Ward on the night of Nov. 20, 2015.

The three are Daniel Kelly, 44, Joe Chappell, 36, and a man aged 19 at the time of the robbery who is now 26, according to the source.

Japanese police identified the men through security camera footage. Japan currently only has extradition treaties with the United States and South Korea.

In the absence of an extradition treaty, the country where a crime was committed usually asks a suspect's home country to prosecute in line with its laws.

Under the British judicial system, an offense is usually tried in the jurisdiction in which it took place.

The men's defense has been arguing that a handover could raise human rights concerns, according to the source.