German prosecutors raided Deutsche Bank AG’s Frankfurt headquarters Tuesday morning in connection with a criminal tax-fraud probe, according to officials and other people familiar with the matter.

The raid came two days after the bank said its co-chief executives would resign but the timing appeared to be unrelated to the management change, people familiar with the situation said.

A Deutsche Bank spokesman said prosecutors hadn’t brought forward any allegations against the bank’s current staff in relation to Tuesday’s events and declined to comment further. Another person familiar with the investigation said some current or former Deutsche Bank staff were drawing prosecutors’ interest.

According to people familiar with the matter, government officials remained throughout the morning at Deutsche Bank’s Frankfurt offices collecting documents and other information in connection with a broad probe into what was described as serious tax fraud involving a number of firms and individuals.

Juergen Fitschen Anshu Jain, co-CEOs of Deutsche Bank

Juergen Fitschen and Anshu Jain, recently resigned co-CEOs of Deutsche Bank.

People close to the investigation said prosecutors were examining what role Deutsche Bank and its clients played in controversial “dividend arbitrage” trades that have been used by a wide range of financial firms and investors to reduce taxes on stock dividends by taking advantage of loopholes in European tax law.

The German prosecutors have been focused on a type of dividend-arbitrage strategy known as “cum/ex,” which were done using dividend-paying shares, the people said. The strategy has been employed using shares issued by companies in Germany, Austria and a handful of other countries. Other legal battles have played out, including in Switzerland, tied to tax refunds paid by their governments stemming from dividend-tax trades.

The Wall Street Journal previously reported that German prosecutors’ probe into the trades has been widening, drawing on help from tax authorities in the U.K. and other countries, and private tax-processing agents.

The term “cum/ex” refers to the timing of the transactions around dividend payments, when the market value of the shares declines after the dividend is no longer factored into the price.

In past years, investment firms and banks used the carefully coordinated cum/ex trades to claim rebates on withholding-tax payments despite not having actually paid such taxes in the first place, according to market participants, lawyers and others familiar with the trades.

Deutsche Bank shares fell 2.5% on news of the raid.

The events reflect persisting woes for Deutsche Bank management as the lender contends with a range of investigations into questionable behavior.

The market for German cum/ex trades largely died off in 2011, when tax authorities closed loopholes and exchange officials fine-tuned how they handled certain transactions, making the trades less-profitable. Cum/ex trades continued on a smaller scale in other countries, but have subsided, market participants say.

Deutsche Bank tax fraud probe Franfurt

Prosecutors on Tuesday collected documents at Deutsche Bank’s headquarters in Frankfurt, Germany.

Deutsche Bank was among a number of active cum/ex market participants for several years and employed some traders who went on to start funds specializing in the trades, according to traders and brokers familiar with the transactions and trading documents reviewed by the Journal. The bank provided financing for some clients to carry out the strategy, including with asset-management firms that catered to wealthy individuals, the market participants said.

Other European and global banks were also active in cum/ex trades, helped by close relationships with wealthy European investors and fund managers geographically located to take advantage of quirks in tax rules. A Deutsche Bank spokesman didn’t comment on the bank’s past cum/ex activity.

German prosecutors and tax authorities have been pursuing a yearslong investigation of cum/ex trades, alleging that firms fraudulently obtained hundreds of millions of dollars’ worth of tax benefits. German authorities have sought help from other European governments, including in the U.K., to gather information about specific trades and clients, the Journal reported last year.

Fallout from the trades intensified in recent months as a U.S. trade-processing firm, acting on the request of German tax authorities, sought detailed trading records in December from Bank of America Corp.’s London-based Merrill Lynch International unit, the Journal reported earlier this year.

A Bank of America spokesman didn’t immediately comment on the status of the investigation.

Before German tax authorities cracked down on the cum/ex strategy, some small firms routinely made hundreds of millions of dollars from the trades, industry officials say. The trades often relied on a practice known as “looping,” which involved shuttling shares among multiple parties around the time of scheduled dividend payments.

The aim was to amass tax claims in excess of what investment firms were actually entitled to declare. Banks typically earned a share of whatever profit their clients earned, market participants say. Some banks routinely extended close to $1 billion in financing to individual firms to amplify cum/ex trades, according to industry officials and fund documents reviewed by the Journal.

The cum/ex trades were a particularly controversial variety of dividend-arbitrage tax trades that remain prominent in Europe. Dividend arbitrage isn’t itself illegal; however, U.S. authorities have been investigating some of the strategies to determine whether trades were conducted on an arm’s-length basis and whether prices of securities reflected true market levels, the Journal has reported.