UPDATED 12/15/11 12:19 p.m.

CHICAGO (CBS) — A woman who blames a nephew of retired Mayor Richard M. Daley for her son’s death wants a special prosecutor to investigate.

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At a news conference Thursday at the Northwestern University Law School, 375 E. Chicago Ave., Nanci Koschman asked for justice at a news conference.

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Daley’s nephew, Richard J. Vanecko, reportedly hit Nanci Koschman’s son, David Koschman, in the face outside a bar in the Rush and Division Street nightclub district in April 2004. Koschman fell and hit his head, and died just days later.

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Nanci Koschman’s new petition claims that early on the morning of April 25, 2004, words were exchanged between Vanecko and David Koschman on Division Street, and then Vanecko punched Koschman.

The case was reopened and closed by Chicago Police earlier this year, without criminal charges. Police said they determined Vanecko acted in self-defense. Detectives reportedly determined Koschman was the aggressor, based on witness accounts.

But those witnesses now say they never told police Koschman was the aggressor.

The office of Cook County State’s Attorney Anita Alvarez also declined to press charges, saying there was not enough evidence to sustain criminal charges against Vanecko. But in March, Alvarez did ask Illinois State Police to examine the Chicago Police investigation.

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The petition notes irregularities in the investigation, including false official reports and a case file that went missing, and says the investigation might have been influenced by Vanecko’s relationship to Mayor Daley. It says the irregularities require an independent investigation.