Tokyo police suspect someone on the inside copied Softbank Corp. client data late last year for three people under arrest for alleged extortion, police sources said Wednesday.

Hiroshi Mori, a 67-year-old publisher, and two others were arrested Tuesday on suspicion of attempting to extort billions of yen from Softbank by threatening to publish data on subscribers to the Internet investor’s Yahoo BB Internet connection service.

The police believe it would take 40 to 50 minutes to copy that much data, even using high-speed equipment. And they have found no sign of unauthorized access to Softbank’s customer database from outside the company, according to the sources.

Given such evidence, the police suspect a person authorized to have access to such data was responsible, according to the sources.

Softbank officials said database access records have allowed them to identify the time when client data were copied late last year.

Only system development employees at Softbank have direct access to the client database, and their numbers have declined from 132 last autumn to 58 at present, according to the officials.

Tokyo police alleged that Mori, who had represented a political organization in the past, obtained the copied data and instructed his colleague, Seiji Takeoka, 55, to use the data for extorting money out of Softbank.

Takeoka and Teruaki Yuasa, 61, were arrested Tuesday with Mori.

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