As part of the investigation, around 10 homes and several offices of individuals and businesses across the country were searched earlier this week, the prosecutors said, adding that there were suspicions of serious tax fraud.
On Tuesday, Deutsche Bank had said that a number of its offices in Frankfurt were searched but that prosecutors were looking for evidence of wrongdoing by clients, not bank employees.
The allegations centre around so-called "dividend stripping", a strategy for tax rebate where a stock is bought just before losing rights to a dividend then quickly sold.
For years, customers exploited a legal loophole which allowed both the buyer and the seller of a stock to reclaim capital gains tax in Germany. But that loophole was closed in 2012.
The raids on Tuesday made front page news as just two days earlier Deutsche Bank had announced that its two chief executives, Anshu Jain and Jürgen Fitschen, were stepping down early following criticism of their handling of repeated scandals and poor profitability at the bank.