Journalist Kostas Vaxevanis, who gained international prominence last year after publishing in his Hot Doc magazine the Lagarde list of Greeks with accounts at HSBC in Geneva, claims that he has the USB stick to which the names were transferred from the original CD supplied by French authorities.
Vaxevanis told followers on Twitter on Wednesday night that he had submitted the memory stick for analysis, which shows "when and how" the list was transferred from the CD to the device.
The journalist also claimed that he had been trying to give the USB stick to financial prosecutor Grigoris Peponis for the last four days but the official had "not shown interest."
Ex-finance minister Giorgos Papaconstantinou admits transferring the data to a USB but denies deleting information relating to three accounts held by his relatives.
Earlier on Wednesday, it emerged that checks on a memory stick held by prosecutors that was handed to them by Papaconstantinou's successor, the current PASOK leader Evangelos Venizelos, in October showed it had been created in July 2011.
This was after Papaconstantinou left office and before Venizelos was given the device by the head of the Financial Crimes Squad (SDOE) Yiannis Diotis, who is to face prosecutors on Monday.