ZURICH (Reuters) - Zurich Insurance said on Monday its finance chief Pierre Wauthier was not subjected to "undue pressure" before he committed suicide and its chairman admitted he was unable to explain the motivation for his tragic decision. Offering conclusions of an investigation into Wauthier's death, the insurer hopes to draw a line under a rocky two months after the 53-year-old finance chief wrote a suicide note saying the then chairman Josef Ackermann had put him under pressure. "We are still deeply saddened by the loss of Pierre Wauthier and we are unable to explain the motivation behind his tragic decision," Zurich Chairman of the board of directors, Tom de Swaan, said in a statement on Monday. Ackermann, the former head of Deutsche Bank