SWITZERLAND - The corruption scandal at the Canton of Zurich civil servants fund (BVK) has taken another dramatic turn, as yet another arrest has been made.

According to the public prosecutor's office, the arrest of the unnamed suspect was made on "suspicion of corruption", while the former head of asset management at BVK and Walter Meier - founder and chief executive of private equity firm BT&T - remain in custody for "danger of collusion".

The public prosecutor said it had also widened the scope of its investigation to include another six people, all of whom work for companies to which BVK has awarded mandates.

It also claimed that the arrested former BVK manager had received "six-figure sums in cash" from Meier on multiple occasions.

The public prosecutor's office said there was "strong suspicion" the former BVK manager had also received other "benefits" since 1997 and up until 2010, including expensive dinners and travel.

The prosecutor said its investigation now included a former member of the administrative board at venture capital firm HBM BioVentures, which allegedly paid the former BVK manager "a six-figure sum" in 2001.

It also claimed some of the mandates awarded by the former head of asset management at BVK had led to conflicts of interest.

While the public prosecutor's office noted that all people under investigation remained innocent until proven guilty, it claimed that most allegations against the former BVK head of asset management were by now "undisputed".

In recent weeks, it has seized more than 2,000 file binders, as well as electronic data, during 17 house searches, while 12 people have been questioned.

Meanwhile, BVK has appointed external legal expert Georg Müller to look into the fund's organisation and corporate governance.

Müller has been professor for constitutional law at the University of Zurich from 1979 to 2006 and authored numerous legal opinions for Swiss federal, local and cantonal authorities.

He is to check "which organisational preconditions could have abetted corruption", according to the Canton of Zurich finance department.

For other parts of the investigation, including the awarding of mandates, an auditing firm will be appointed in the coming weeks.