(CBS) A federal judge says Zacarias Moussaoui, the only person charged in the United States with conspiring to carry out the Sept. 11 terror attacks, is mentally competent to fire his court-appointed lawyers and represent himself at trial.

U.S. District Judge Leonie Brinkema, however, asked Moussaoui's current lawyers to remain in the case even though they pleaded for her to dismiss them. Moussaoui has contended his attorneys are part of a conspiracy to kill him.

During his court appearance Thursday, Moussaoui denied that he played any role in the attacks.

He said the federal government "knew I was not in contact with these people who were to have done the hijacking."

Moussaoui, who was at the lecturn to answer questions from the judge about his legal representation, kept asking Brinkema for a chance to reveal a secret that would compel the government "to withdraw the case today."

The judge repeatedly tried to cut him off, telling Moussaoui at one point that "we're not here for speeches." But near the end of the trial, the defendant was allowed to address the charge that he conspired with the hijackers to carry out the September attacks.

Moussaoui lived in Norman, Okla., last year while taking flying lessons, but he never received a pilot's license.

He was arrested Aug. 16, when officials of another flight school became suspicious of his behavior. He told the judge the government "knew who I was when I entered the United States of America and decided to arrest me."

Moussaoui said the government's knowledge that he had no connection to the hijackers was related to information learned several years ago, when British authorities raided the address where he lived in London: 23-A Lambert Road, FW 2.

Moussaoui said that because of the raid, the U.S. government had launched an undercover surveillance operation against him.

Brinkema, in granting Moussaoui's request to represent himself, said his decision was "unwise but rational," adding that she agreed with a court-appointed psychiatrist that Moussaoui was mentally competent to make the decision.

Moussaoui, 34, a French citizen with a master's degree, wore a green jumpsuit with "prisoner" stamped on the back. He entered the room with U.S. marshals and initially was seated by himself at a separate table to the right of his court-appointed attorneys in the packed courtroom.

Moussaoui's mother, Aicha el-Wafi, who lives in France, attended the hearing, sitting in the second row with a black scarf covering her head.

Moussaoui told the judge that he has been contacted by a Muslim lawyer, who he said agreed to assist him in the case, for which jury selection is expected to commence in late September.

Brinkema said, however, this could happen only if the lawyer met court admission procedures for attorneys.

Government prosecutors did not object to Moussaoui's request for self-examination, but argued that the current court-appointed lawyers should remain in the case because of their expertise.

However, federal public defender Frank Dunham Jr. pleaded with the judge to dismiss him and his team.

"It's not fair to him" to keep the current lawyers in the case because of "this belief we're trying to kill him," Dunham said.

Outside the courtroom, Dunham told reporters he and his associates on the defense team were puzzled by Moussaoui's determination to release them.

"We were working as hard for this man as we know how to do as defense attorneys," he said. "We don't know why Mr. Moussaoui believes the way he does. It's that belief that caused us to question his mental status and ask for the exam."

Another defense lawyer, Edward McMahon Jr., said, "We don't believe, and we still don't believe, that Mr. Moussaoui can get a fair trial, given the conditions of his confinement."

In advance of Thursday's hearing, a court-appointed physician, Dr. Raymond Patterson, concluded that Moussaoui was not suffering from a mental illness when he asked to fire his lawyers and represent himself.

Earlier in the week, Moussaoui lost a round in court when the same judge denied him access to any sensitive aviation security information during his trial.

Prosecutors had asked the judge to bar Moussaoui's lawyers from passing on any printed information on aviation security or telling him about it in private. In a motion, prosecutors argued that the information was on the same level as national security information and the release of it would be "detrimental to the safety of passengers in transportation."

The information should only be distributed to those with an "operational need to know," the motion said.

Brinkema's ruling Tuesday was the first time Moussaoui has been barred from obtaining information to conduct his defense. The charges he is facing could result in the death penalty.