Congressional investigators think that reams of internal documents turned over by Bank of America last Friday show that its executives were alarmed by mounting losses at Merrill Lynch well before shareholders voted to approve the merger, according to sources familiar with the matter.

Investigators also think the documents, combined with prior testimony and fresh interviews with a key executive, suggest that Bank of America chief executive Kenneth D. Lewis used the threat of backing out of the government-backed deal as leverage for billions more in taxpayer bailout money, the sources said.