Current and former executives at Credit Suisse, stretching from New York to the Swiss lender’s top ranks in Zurich, are sparring over who was responsible for the bulk of almost $1 billion in losses in recent months, according to people familiar with the matter.

One particular point of dispute: Past and present top executives of the investment bank have given differing accounts of who was in charge of what during a critical period for the loss-making trading business late last year.