Investigators questioning how some people managed to contribute thousands to Mayor de Blasio Campaign

NEW YORK (WABC) -- A copy of a bank check written to 'New Yorkers for de Blasio' from Rafael Zepeda in the amount of $5,000 was released on Friday by the Campaign Finance Board. Paperwork there shows Zepeda could not attend an October 2013 fundraising event, but 'would still like to support Bill and contribute that $5,000'.

There is also another check to 'New Yorkers for de Blasio' also for $5,000 from a Jose Zepeda. No one answered at the Zepeda's apartment on Friday, but Eyewitness News now know investigators are questioning whether it was their money or someone else's.

"It should definitely raise a red flag - if you look at one's lifestyle, and see how can he make such a huge contribution," said Dick Dadey of Citizens Union, "You have to look then at the source of that contribution. Did he act as a straw donor, in a sense, making a contribution on behalf of somebody else?"

Mayor Bill de Blasio has steadfastly said he and his campaign have done nothing wrong.

"Anyone who donates to me, or to any cause associated with me can have no expectation of any special favor in return. We don't allow that - we don't accept it," de Blasio said.

City Hall said it is not part of the investigation, but acknowledged Press Secretary Karen Hinton, on the job for only 10 months, has resigned. On the radio Friday, the Mayor complained of so many investigations - into his fundraising for Democratic Senate candidates in Albany, whether he fought to ban horse carriages because of huge contributions from animal rights activists - and now the question about straw donors.

"I'm really concerned about a double standard here, where we do everything to the letter of the law, disclose everything, we are open about it, do not let it affect our decisions. Meanwhile, a lot of people are doing a lot worse, and not getting much examination," said the Mayor.

Dadey says that it has all become a 'cesspool' for the Mayor.

"It all speaks to a pattern of behavior that he's not paying that much attention to the way in which he raises money for causes," Dadey said.