Confusion surrounds the motive for Josef Ackermann's resignation as chairman of Zurich Insurance Group after reports in the Swiss press that he had been preparing to leave before he became embroiled in controversy over the suicide of Pierre Wauthier, the firm's chief financial officer.

Wauthier's suicide note is said to reference a difficult working relationship with Ackermann and Zurich bosses have launched an investigation to see if their late CFO was placed under any "undue pressure".

When Ackerman quit as chairman, he issued a statement saying he had reason to believe Wauthier's family partly blamed him for the suicide, but dismissed any allegations as "unfounded". He also said he was "shocked" by the death and his resignation was to help protect Zurich's reputation.

However, there has been speculation in the Swiss press from anonymous sources that Zurich's recent poor performance - it reported a sharp 27% fall in profit during the second quarter - had led former Deutsche Bank chief executive Ackermann to contemplate quitting even before Wauthier's suicide.

According to one person, quoted by The Times, who said they had spoken to senior Zurich executives, several people "are wondering if the suicide is enough of a reason to resign", despite Ackermann's statement which suggests the death was the catalyst.

Speaking to Swiss newspaper Neue Zürcher Zeitung, Zurich Chief Executive Martin Senn said Ackermann stepping down was an "entirely personal decision".

He refused to be drawn on the content of Wauthier's suicide note, other than it was about Ackerman's behaviour from the CFO's view, saying it would be "inappropriate".

After reports that Wauthier's widow had been silenced by Zurich from speaking out, Senn said the firm had placed "absolutely no restrictions in terms of what she may say and what not" and "we would never give speech bans".

Senn added that she had been abroad when her husband died, and their two children were studying in different countries, so Zurich helped bring them together.

There had been a report previously in the Swiss media that Wauthier's widow planned to read from her husband's suicide note at his funeral, which had prompted Ackermann's resignation.