Bill de Blasio met with federal prosecutors in a Manhattan law office on Friday where he faced questions related to a criminal probe of his fundraising, the mayor’s office said. Prosecutors have been investigating whether or not donors to de Blasio’s 2013 campaign or his former nonprofit, Campaign for One New York, were rewarded with favors. De Blasio, who agreed to speak voluntarily and without immunity to prosecutors, arrived at Kramer Lefin Naftalis & Frankel LLP, the firm of his defense lawyer Barry Berke, just after 9 a.m.