The former chief executive of Raiffeisen bank in Switzerland, Pierin Vincenz, has spoken out against his 15-week confinement behind bars. Vincenz was released on Wednesday but still faces a criminal investigation into alleged fraud, which he denies committing.

In a statement, Vincenz called his detention period "unnecessary and completely disproportionate in its length". He and a former business partner, who was also released at the same time, were held while Zurich prosecutors gathered evidence.

In February, Vincenz was accused of illegally enriching himself by making personal investments in two Raiffesisen subsidiaries, Aduno and Investnet. Raiffeisen bank has also joined the criminal probe as a complainant.

Vincenz, who headed Raiffesisen from 1999 to 2015 during a period of expansion, has been forced to step down from various other business roles since the investigation began. He has resigned as chairman of Swiss insurance group Helvetica and relinquished a similar position at power group Repower in recent months. He was also chairman at Aduno during the period under investigation.

Zurich prosecutors on Wednesday stated that the investigation is “well advanced”. Vincenz said he would continue to robustly defend himself against the allegations.

Raiffeisen is Switzerland’s third largest banking group after UBS and Credit Suisse and one of four banks that the Swiss financial regulator considers “too big to fail”.