Challenging the request of Zachary Warren, the former client relations manager at Dewey & LeBoeuf, to sever his case from co-defendants, the Manhattan District Attorney’s Office claims Warren was “a willing foot soldier” motivated by a large bonus who helped the firm’s senior management to implement a fraudulent scheme that led to the firm’s demise.

Warren filed a severance motion to be tried separately from former Dewey leaders Steven Davis, Stephen DiCarmine and Joel Sanders. All four have pleaded not guilty. Warren argued there is a risk of “guilt by association” at trial and said he never expected to face criminal charges resulting from his two-year post-college stint at Dewey.

But Assistant District Attorney Peirce Moser, in a response filed Friday, said that during an interview last November, Warren asked prosecutors if they were offering him immunity. “Warren was also told that if his memory improved or if he retained counsel, he should reach out to the People, and we would start with a clean slate,” Moser said. “[He] chose not to act on the People’s invitation, so it is hard to imagine where else he expected to be standing at this point.”

Though Warren was not the mastermind of the Dewey fraud scheme, Moser said Warren helped Sanders and Francis Canellas, the ex-finance director who has already pleaded guilty, develop a plan about fraudulent accounting methods during a steak dinner. Sanders told Warren that he would receive his full bonus if Dewey met its bank covenants, Moser said.

The prosecutor also charged that Warren helped disseminate a lie “to keep the partners at bay and further perpetuate the scheme,” and that even after he left Dewey in mid-2009 to attend law school, Warren insisted “that he be compensated for his criminal activity.”

William Murphy, a partner at Zuckerman Spaeder who represents Warren, declined to comment. Warren will reply by June 23.