The National Black Police Association (NBPA) questioned whether Scotland Yard had a "vendetta" against Mr Dizaei.
The law firm reviewed NBPA documents and emails, and interviewed more than three dozen witnesses.
However, Mr Nhanda denied the NBPA's stance had caused a rift among the Met's ethnic minority associations.
Billy Hunter was terminated by Derek Fisher and the NBPA after acting as Executive Director for seventeen years.
The investigation comes in the wake of a public feud between the NBPA's president and its executive director.
It began last April and included reviews of documents, financial records and NBPA emails, and interviews of witnesses.
On Wednesday news that Supt Dizaei would not face disciplinary action was welcomed by the NBPA's vice-president, Clive Morris.
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"In my work for the NBPA, my priority has always been to promote the interests of the players, " Hunter wrote.
The NBPA has been calling for an inquiry into the Dizaei case but Mahesh Nhanda said the boycott call was "blackmail".
On May 16, Billy Hunter filed the aforementioned lawsuit against the NBPA, Fisher and Wior, which enumerates twelve separate causes of actions.
The NBA and NBPA scheduled to continue their deliberations with small parties on Monday, then again with the full cast on Tuesday.
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The NBPA had called for a boycott of the police force by ethnic minority recruits as talks over the officer's future broke down.
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Hunter is claiming that Fisher stated that Hunter had divided, misled, and misinformed the NBPA and players and propounded threats and lies against the Union.
Since then, the NBPA has demanded Mr. Fisher's resignation as president.
His firing occurred when Fisher and the other members of the NBPA Executive Committee sent Hunter a letter notifying his that he was terminated, effective immediately.
He also takes a thinly veiled shot at NBPA Executive Director Billy Hunter, wondering if his main interest lies in protecting his own turf above all else.
The PCA's decision to force the Met to make Mr Dizaei face a tribunal led to a threat of protest action by the National Black Police Association (NBPA).
BBC: NEWS | UK | England | London | Cleared officer escapes tribunal
After allegations surfaced about the organization's finances in recent weeks, NBPA president Derek Fisher, a player for the Oklahoma City Thunder, called for a financial review of the union's books.
Hunter also states in the letter, obtained Tuesday by The Associated Press, that the NBPA will no longer work with Prim Capital, the banking firm that employs Hunter's son, Todd.
Through an NBPA spokesman, Mr. Hunter denied any wrongdoing.
In other words, even if a court essentially believes the dissolution of the NBPA to be a tactical ruse, it may not matter if enough players seeking damages were non-union members anyway.
Now that this has occurred, I will continue to examine all of my options, including whether the fairness that was absent from the NBPA process might be available in a different forum.
"It is no secret that in recent weeks, the leadership, finances and business practices of the NBPA have been questioned, " the organization said in a statement that acknowledged the subpoena and the investigation.
"NBPA Executive Director Billy Hunter has pledged his full cooperation with the internal inquiry, although he has recused himself from the process to ensure that it is an independent one, " the NBPA's statement said.
The NBPA's demand for his resignation was motivated by its "need to protect the NBPA management and their own best interests instead of protecting the players, " Mr. Fisher said in a statement issued on Friday.
Mr. Hunter's pattern of involving friends and family in union business contributed to a deep rift among the NBPA staff, " the report said, adding that Hunter's choices "created the appearance that he operated the union in part for the benefit of his family and friends.
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