The investigation focused on de Blasio's 2013 campaign fundraising practices, especially alleged quid pro quo contributions. During his weekly appearance on a local radio show, de Blasio said he appreciated that both prosecutors had completed a "thorough" effort and made their conclusions public.
Mayor Bill de Blasio broke state law when he and his subordinates steered money towards Democratic state senate campaigns - but he can't be charged with a crime because his lawyer said it was OK, according to the Manhattan District Attorney's office.
In a "rare" statement about the status of an investigation, the United States Attorney for the Southern District of NY said the office, along with the FBI, had looked into donations solicited by de Blasio's 2013 campaign and others "from individuals who sought official favors from the city, after which the mayor made or directed inquiries to relevant city agencies on behalf of those donors".
Minutes after Vance's statement, the U.S. Attorney's Office in Manhattan said it was also ending a separate investigation into whether official favors were done for campaign donors.
Experts on NY politics said they couldn't think of a comparable situation in which the city's mayor had faced a probe - and had been questioned - by federal prosecutors. Vance took the unusual step of noting instances when the mayor appeared to toe right up to the line of legality, and he described the mayor's actions as contrary to the "intent and spirit of the law".
New York Mayor Bill de Blasio speaks during a news conference at Rikers Island jail in New York City, U.S. September 1, 2016.
But he emphasized that the lack of an indictment did not mean an endorsement of the mayor and his aides' behavior, which he said violated the spirit and intent of the campaign finance law and its contribution limits.
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Mayor Bill de Blasio and his aides will not face criminal prosecution in connection with his campaign fund-raising, prosecutors announced Thursday.
De Blasio, who is up for re-election later this year, has denied wrongdoing. "What matters is the fact that this was extensively investigated for a year, and no charges have been brought".
It centered on solicited donations from individuals who sought official favors from the city.
The money was then transferred to the candidate groups, which then used them on things like consultants and media advertising, a shift that "often occurred within days", Vance said.
The Manhattan District Attorney's office says it will not prosecute the administration because they relied on legal advice from their attorneys during the process.
"After careful deliberation. we do not intend to bring federal criminal charges against the Mayor", said Kim, who replaced U.S. Attorney Preet Bharara - fired Saturday by President Donald Trump.
While his ethics were called into question, de Blasio did not want to respond to several questions tossed in his direction in what he called were "characterizations by DA Vance".