The battle between the Federal Reserve and Trump administration prosecutors accelerated over the past few weeks amid mixed signals and mutual suspicion, according to interviews with a half-dozen figures with knowledge of the dispute. Late last month, Federal Reserve officials grew concerned that the Justice Department was preparing a criminal case against them when they received two casually-worded emails from a prosecutor working for Jeanine Pirro, the U.S. attorney in Washington. The messages sought a meeting or phone call to discuss renovations at the central bank's headquarters, according to three people familiar with the matter, who like most others interviewed spoke on the condition of anonymity to discuss an open investigation.