The lawyers asked a judge in Manhattan Monday to bar all the statements Manssor Arbab-siar made to investigators during interrogation.
In the filing, two experts retained by the defense each said they had diagnosed Arbabsiar with bipolar disorder.
Arbabsiar, 56, a former used-car dealer from Corpus Christi, Texas, was arrested last fall and was said to have confessed to his role during the first 12 days he was in custody and before he got defense counsel.
Prosecutors have said Arbabsiar “knowingly and voluntarily” waived his rights to remain silent, to have a lawyer present and to be quickly taken before a judge. But the filing shows the defense will challenge whether those decisions were voluntary.
Dr. Michael B. First, a professor of clinical psychiatry at Columbia University, said he had concluded that Arbabsiar “was likely cycling in and out of manic episodes during the period” of his interrogation. Professor First said he had examined Arbabsiar several times at the Metropolitan Correctional Center, where he is being held pending trial.
“Because I believe that Mr. Arbabsiar was suffering from episodes of mania while he was being questioned by the FBI,” Professor First wrote, “there are serious questions as to whether any decisions made by him during this period were made rationally, with a full understanding of the consequences. Indeed, it is likely that his decisions were influenced, at least in part, by his mental illness.”
He said individuals with bipolar disorder who are in a manic state often “display feelings of invincibility and grandiosity,” and such feelings “may cause them to enter into agreements that they would not otherwise enter into.”
Arbabsiar’s trial is due to start October 22.