DETROIT (AP) — Wearing a T-shirt, khaki-style pants and a chain at his ankles, a somber-looking Nigerian man accused of trying to blow up a U.S. airliner on Christmas said he understood the charges against him, triggering the defense of a criminal case that could lead to life in prison.

Umar Farouk Abdulmutallab’s arraignment in federal court Friday took fewer than five minutes and a not guilty plea was entered on his behalf. The 23-year-old said little, telling the judge simply that he understood the six-count indictment he faces and the maximum penalty.

Abdulmutallab’s first court appearance came exactly two weeks after an Amsterdam-to-Detroit flight in which passengers rushed to his seat and put out flames that could have caused a disaster. The FBI says Abdulmutallab tried to destroy Northwest Airlines Flight 253, which was carrying nearly 300 people, by injecting chemicals into a package of explosives concealed in his underwear.

The alleged attack has shaken up airport security worldwide. President Barack Obama considers it an attempted strike against the United States by an al-Qaida affiliate and faults his administration for not preventing it despite intelligence reports.

A grand jury this week indicted Abdulmutallab on six charges. The most serious — attempting to use a weapon of mass destruction — could land him in prison for life if convicted.

He replied “yes” when asked Friday if he understood the charges and said he had taken “some pain pills” after the judge inquired whether he had used any drugs or alcohol in the past 24 hours. He is being held at a federal prison in Milan, Mich., and had been treated at a hospital for burns.

U.S. Magistrate Judge Mark Randon entered a not guilty plea for Abdulmutallab. It’s a routine practice in federal court for the defendant to allow the judge to enter a plea.

The defense team did not challenge the government’s request to keep Abdulmutallab in pre-trial custody. After the hearing, one of his attorneys declined to talk about the case.

“It’s just too soon in the process to make any comment,” Leroy Soles said at a nearby coffee shop. The date of the next hearing was not set.

A Detroit-area native who sat six rows in front of Abdulmutallab on the plane watched the arraignment from the courtroom gallery. Hebba Aref, who drew international attention in 2008 after being refused a seat directly behind then-candidate Obama at a Detroit rally because she was wearing a headscarf, said she wants Abdulmutallab to be “tried by the system” but also is concerned about what his case could mean.

It’s the “whole ideology out there that’s radical and misuses a beautiful religion,” said Aref, 27, a Muslim. “That’s what needs to be dealt with and deterred. … He’s just a small part of it.”

U.S. investigators say Abdulmutallab told them he received training and instructions from al-Qaida operatives in Yemen. His father warned the U.S. Embassy in Nigeria that his son had drifted into extremism in Yemen, but that threat never was fully digested by the U.S. security apparatus.

Maryam Uwais, a lawyer in Nigeria, and Mahmud Kazaure, a lawyer from Maryland, told The Associated Press they were sent by Abdulmutallab’s family to observe Friday’s hearing. Neither have a role in the case but both spoke briefly with the suspect’s legal team. They declined further comment.

Outside the courthouse, authorities set up metal barricades and limited foot traffic. One demonstrator held a sign that read: “No U.S. Rights For Terrorists.”

About 50 men and women identifying themselves as Detroit-area Muslims chanted “We are Americans” as they marched behind the barricades to denounce terrorism. About a dozen of them carried U.S. flags or signs with messages such as “Not in the name of Islam.”

Four Muslims who were part of the protest performed Friday prayers in the court’s small museum on the first floor.

“We have prayer rugs outside in the car. We could have done a show for the media,” protest organizer Majed Moughni said. “We’re doing this for God.”

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Associated Press writers Mike Householder and Jeff Karoub contributed to this report.