(Changes sourcing) May 4 (Reuters) - U.S. Senator Elizabeth Warren has accused First Republic Bank executives of "mismanagement" in a letter to its former CEO Micahel Roffler and raised questions on the failed lender's risk management as well as pay and bonuses. "You owe your customers and the public an explanation for the decisions that resulted in the costly failure of your bank," the Democrat wrote in the letter dated Wednesday, which was made public by her office. Regulators seized troubled First Republic Bank and JPMorgan Chase agreed to buy majority of its assets earlier this week, marking the largest U.S. bank failure since the 2008 financial crisis. "The primary cause of the collapse...appears to be complacency, incompetency, and mismanagement by you and other bank executives," Warren said. Roffler has been asked to submit responses by May 17. He could not be reached for comment on Thursday. The contents of the letter were first reported by the Wall Street Journal.