BOSTON – His arm in a cast and his face swollen, a blasé-looking Dzhokhar Tsarnaev pleaded not guilty Wednesday in the Boston Marathon bombings during a seven-minute proceeding that marked his first appearance in public since his capture in mid-April.

As survivors of the bombings watched, Tsarnaev, 19, gave a small, lopsided smile to his two sisters upon arriving in the courtroom. He appeared to have a jaw injury, and there was swelling around his left eye and cheek.

Leaning into the microphone, the Russian immigrant told a federal judge, “Not guilty,” and repeated it as the charges were read. Then he was led away in handcuffs, making a kissing gesture toward his family. One of his sisters sobbed, resting her head on a woman seated next to her.

Tsarnaev, who has been hospitalized since his capture with wounds suffered in a shootout and getaway attempt, faces 30 federal charges, including using a weapon of mass destruction to kill, in the April 15 attack, which left three people dead and more than 260 wounded. He could get the death penalty if prosecutors choose to pursue it.

The proceedings took place in a heavily guarded courtroom packed not only with victims but with their families, police officers and members of the public and the media.

Karen Brassard, a 51-year-old homemaker from Epsom, N.H., attended the arraignment. Her left ankle and right leg were injured in the bombings. Her daughter and husband were also injured and a friend who was with Brassard at the time lost both of her legs.

She hasn’t decided, though, whether Tsarnaev should get the death penalty. “It depends on the minute; it depends on the day. I have mixed emotions,” she said afterwards. “I get angry, but I also think he’s just a kid.”

She will get a chance to make up her mind as Tsarnaev’s case moves toward a trial that may last three months and have 80 to 100 witnesses. A date hasn’t been set. A line of more than a dozen uniformed Massachusetts Institute of Technology police officers stood at attention outside the courthouse during the arraignment in honor of Sean Collier, a police officer for MIT. Tsarnaev and his brother, Tamerlan, ambushed and killed Collier in his cruiser in an attempt to take his gun and escape three days after the bombings, prosecutors said. Tamerlan died in a gun battle with police.

MIT Chief of Police John DiFava attended the arraignment because he said he wanted to see Tsarnaev. “I wanted to take a look at this guy,” he said after the hearing. “He’s a punk. He’s a typical bad guy.”

DiFava said he favors the death penalty for Tsarnaev. “The man deserves to die if he’s found guilty,” he said.

His two sisters were in court wearing traditional Muslim scarves called hijabs. One was carrying a baby; the other wiped away tears with a tissue. Tsarnaev’s parents remained in Russia.

Tsarnaev’s lawyer, Judy Clarke, an expert in death penalty cases, asked that the judge enter not-guilty pleas for him, but U.S. Magistrate Judge Marianne Bowler said: “I would ask him to answer.”

Meanwhile, Boston Police Commissioner Edwards F. Davis III appeared on Capitol Hill and complained to a Senate panel that the Justice Department failed to share information on threats with local officials before the bombings.

“There is a gap with information sharing at a higher level while there are still opportunities to intervene in the planning of these terrorist events,” Davis said.

Reporters and spectators began lining up for seats in the courtroom at 7:30 a.m. as a dozen Federal Protective Service officers and bomb-sniffing dogs surrounded the courthouse. Four hours before the 3:30 p.m. hearing, the defendant arrived at the courthouse in a four-vehicle motorcade.

About a dozen Tsarnaev supporters cheered as the motorcade arrived. The demonstrators yelled, “Justice for Jahar!” as Tsarnaev is known. One woman held a sign that said, “Free Jahar.”