Ex-Nissan chief Carlos Ghosn, who is awaiting trial in Japan, urged on Thursday a Tokyo court to dismiss the case against him, accusing Japanese prosecutors of a "pervasive pattern of illegal misconduct".
The claims, made in two filings to the Tokyo District Court by his lawyers, allege prosecutors colluded with Nissan and effectively subcontracted out their investigation to employees of the automaker who were trying to oust Ghosn.
"The court filings demonstrate that the prosecutors' case, which was politically motivated and poisoned from the start, is fundamentally flawed and contradicted by the evidentiary record," Ghosn's lawyers said in a statement.
Ghosn is out on bail in Tokyo, awaiting trial on four charges of financial misconduct. He denies any wrongdoing and laid out his defense again Thursday.
But he and his lawyers argue the entire case against him is "fundamentally flawed".
The filings allege the creation of a "secret task force" at Nissan created to "drum up allegations of wrongdoing by Mr. Ghosn as a pretext to remove him".
They formalize claims Ghosn has made previously -- that the allegations against him stem from resentment within Nissan over his plans to more closely integrate the firm with its alliance partner, French automaker Renault.
Along with Mitsubishi Motors, Nissan and Renault form a leading auto alliance, but relations inside the partnership have been tense at times.
Ghosn's legal team claim the opposition to further integration of the car firms drew in even government officials from the Ministry of Economy, Trade and Industry (METI).
"The prosecution against him resulted from unlawful collusion between the prosecutors, government officials at METI, and executives at Nissan," Ghosn's legal team said in a statement.
They wanted to prevent Ghosn from further integrating Nissan with its French alliance partner Renault SA, according to the lawyers.
Ghosn's legal team accuses prosecutors of wide-ranging misconduct, ranging from claims they used Nissan employees to investigate and even seize the former tycoon's property, to accusations of discrimination and denying him a speedy trial.
The formerly high-powered executive was detained last November as he landed in Tokyo on a private jet, and spent 108 days in detention before winning bail.
He was rearrested not long afterwards, as prosecutors added to his charge sheet, but won bail for a second time after spending another 21 days in detention.
His release came with strict conditions, including restrictions on seeing his wife and bail of $4.5 million.