Investigators suspect managers at Deutsche and other banks of helping to exploit a loophole which allowed two parties to claim ownership of the same shares, making it possible to claim dividend tax rebates running to billions of euros.

The scheme, called "cum-ex", involved several other global banks.

The Cologne prosecutor's office is also probing Garth Ritchie, the head of Deutsche Bank's investment banking arm, as part of the investigation, Sueddeutsche Zeitung reported on Thursday, citing unnamed sources. Ritchie, through a Deutsche Bank spokesman, declined to comment.

Jain, through a personal spokesman also declined to comment. Deutsche Bank declined to comment on whether Jain, who was co-CEO from June 2012 to June 2015, was included as part of the probe.

The scam, which for years operated in a legal grey area until prosecutors declared it to be fraudulent, is being investigated by several prosecutors' offices including by officials in Cologne.

The Cologne prosecutor could not be reached for comment.

In a statement, Deutsche Bank confirmed that current and former managers were under investigation, but did not say who they were.

Deutsche Bank said that the Cologne prosecutor had been investigating two former employees since 2017 in connection with cum-ex transactions on behalf of former clients.

Deutsche Bank said the lender was not directly involved in the tax scheme.

"Recently, the prosecutor has initiated investigations against further former and current employees and management board members," it said in a statement.

It said the change in approach by the Cologne prosecutor was linked to procedural issues related to the statute of limitations, and did not imply that the prosecutor had changed its view on the facts of the case.

"This has also not changed the Bank's assessment of the facts of the case. Deutsche Bank did not participate in an organised cum-ex market, neither as short seller nor as cum-ex purchaser," Deutsche said.

Deutsche Bank acted as a leverage provider to clients who were involved in the scam, Handelsblatt reported.

Sueddeutsche Zeitung said that fraudulent tax claims related to the 2009 business year, running to more than a billion euros, would expire soon unless prosecutors press criminal charges.

Reuters reported in January that investigators had found indications that senior managers had discussed the reputational risks related to the cum-ex scheme, which sparked Germany's biggest post-war fraud probe.

(Reporting by Edward Taylor, Andreas Framke, Douglas Busvine and Hans Seidenstuecker; Editing by Alexandra Hudson and Susan Fenton)