In a motion filed in court last week, Hosam Smadi's lawyers say FBI agents didn't advise him of his right to remain silent until they had questioned him for seven minutes. The motion says Smadi tried to stop speaking with the agents, but that their questions continued for several hours.
Mark White, a spokesman with the FBI bureau in Dallas, said Wednesday that he had no comment. The FBI routinely does not comment about active cases.
Prosecutors have yet to file a response to the motion to suppress Smadi's statements. The case is set for trial next month.
Public defenders Richard Anderson and Peter Fleury accuse the FBI of making an "end-run around Miranda by conducting interrogations by asking questions first and reading the Miranda rights after the suspect has already begun talking."
According to the public defenders, Smadi repeatedly said he didn't want to talk to the agents. Instead, an agent said he would "just like to have a conversation with you, OK?"
The agent, before reading Smadi his rights, tried to put the suspect at ease by asking him general questions about growing up in Jordan and expressing sympathy about the death of his mother, according to the motion.
"They successfully obtained his agreement to talk before the warnings were given," the motion states.
Authorities accuse Smadi of leaving what he thought was a truck bomb in a garage beneath the 60-story Fountain Place building in downtown Dallas in September. The device was a decoy provided by FBI agents posing as al-Qaida operatives.
The FBI said it had been monitoring Smadi after discovering him on an extremist website last year. Investigators say he acted alone and was not affiliated with any terrorist organizations.
In court papers, Smadi's federal public defenders have argued that their client exhibited signs of depression and mental illness when his parents separated and that he "completely fell apart" when his mother died of brain cancer.