NEW YORK (CBSNewYork) -- There was new insight Wednesday into a probe of Mayor Bill de Blasio and allegations of pay to play at city hall.
Investigators found the mayor and top aides used private email to conduct city business, and went to unusual lengths to help a campaign donor.
As CBS2's Tony Aiello reported, the City Department of Investigation -- one of the agencies that investigated the mayor and his treatment of campaign donors -- just released a memo summarizing its probe.
It revealed that de Blasio and top aides sent thousands of private emails to conduct city business.
"It just seems inappropriate to be using personal emails. It also raises questions about 'why.' Are you trying to keep something from the public?" Dick Dadey of Citizens Union asked.
Critics also complained the Mayor Bloomberg used private email to conduct city business.
Now, DOI recommends the city mandate the use of official email accounts.
The DOI memo also revealed new details about the mayor and his donor Harendra Singh who wanted to slash the amount of money he owed for his restaurant on city property.
It should have been a routine negotiation for bureaucrats at a city agency known as D-CAS. Instead, the mayor's office micromanaged the process, and D-CAS workers called it unprecedented.
They were told to 'resolve this matter' because Singh was a 'friend of the mayor.'
Eventually D-CAS was completely cut out and Emma Wolfe, a top aide to de Blasio conducted the final settlement negotiations with Singh's attorney.
"That's the huge takeaway here. not everyone is treated equally at City Hall. If you're a fat cat donor to the de Blasio campaign, you're going to get special attention," Dadey said.
The mayor's republican challenger said it raises a question for voters.
"Are they voting for someone who's honorable, someone doing right by the taxpayers, putting citizens first? Or are they going to put donors and special interests first?" Nicole Malliotakis asked.
A spokesman for the mayor told CBS2's Aiello, "this administration makes decisions based on the facts, and nothing else."
In March prosecutors criticized city hall, but declined to press any charges.
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