MIT Police Chief John DiFava, who was also in the courtroom, said Tsarnaev looked "smug."
"I didn't see a lot of remorse. I didn't see a lot of regret," he said. "It just seemed to me that if I was in that position, I would have been a lot more nervous, certainly scared."
DiFava added: "I just wanted to see him. I wanted to see the person that so coldly and callously killed four people, one of whom being an officer of mine."
Authorities say Tsarnaev orchestrated the bombing along with his older brother, Tamerlan Tsarnaev, who died following a gun battle with police three days after the attack. Dzhokhar Tsarnaev was arrested on April 19, hiding in a bloodstained boat in a suburban backyard after a manhunt that paralyzed much of the Boston area.
Tsarnaev is also charged in the killing of a Massachusetts Institute of Technology police officer and the carjacking of a motorist during their getaway attempt.
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 back 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."
On the same day as the arraignment, Boston's police commissioner appeared on Capitol Hill and complained to a Senate panel that the Justice Department failed to share information on terrorism threats with local officials before the bombing.
"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," Commissioner Edward F. Davis III 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.