Bernd Buhner, a detective involved in the case, stated that the bank had drawn up a plan to monitor as many as 20 people, including a number of investors, the Wall Street Journal reports.
The affair originally came to light in May when the bank said its corporate security department and outside contractors - including Mr Buhner - had been using "questionable investigative or surveillance activities".
So far four incidents have been disclosed, but Mr Buhner told the news source that in 2006 he was given a list of people to spy on by representatives of the financial institution.
"They had the names ready. A paper with the list of names was prepared by the bank in advance of a meeting with bank officials," he told the news source.
An investigation into the matter was opened by German officials last month and the scandal has already led to the dismissal of head of security in Germany Rafael Schenz and investor relations chief Wolfram Schmitt.