Jury selection began this week in the trial of Dzhokhar A. Tsarnaev, the 21-year-old accused of carrying out the Boston Marathon bombing with his older brother. Potential jurors are filing in and out of the federal courthouse in Boston with the goal of finding 18 people (a dozen jurors and six alternates) to serve from among the 1,200 people being considered.

In part, the jury pool is so massive because of the nature of this particular case. If the goal is to find people who can serve as impartial jurors, that means figuring out who may have been influenced by media coverage or by public opinion in the Boston area. Tsarnaev’s attorneys argued that it was impossible to find such a jury in the region, asking that the trial be moved, but District Judge George A. O’Toole Jr. denied that request and said that “a fair and impartial jury” could likely be found. Potential jurors will be given questionnaires and asked questions by lawyers to determine whether they can serve.

The people who are ultimately selected must all share something in common: They cannot be opposed to the death penalty.

“This case is not about guilt,” Daniel Medwed, a law professor at Northeastern University, told NPR. “In my mind, this case is really about whether or not he’s going to get the death penalty.”

This is an unusual situation in Massachusetts, since the state abolished the death penalty in 1984, nearly a decade before Tsarnaev was born. (New Hampshire is the sole state in New England that still has the death penalty.) Over the last three decades, some governors in Massachusetts have tried to reinstate the death penalty; while he was in office, Mitt Romney assembled a panel to create a new death-penalty framework in 2003 and unsuccessfully introduced a bill to revive the practice two years later.

Since that time, the death penalty has grown less popular nationwide. Six of the 18 states to abolish the death penalty have done so since 2007. A majority of Americans still support capital punishment, but the number has dramatically fallen. Last year, the United States executed 35 inmates, the smallest number in two decades. Fewer states carried out executions, while fewer people were sentenced to death.

One of the people who does not support the death penalty is Attorney General Eric H. Holder Jr. He said he opposes the death penalty partly because “dedicated men and women can make mistakes.” But last year, Holder announced that because of “the nature of the conduct at issue and the resultant harm,” the Justice Department would seek the death penalty in the Boston bombing case.

Carmen M. Ortiz, the U.S. attorney for Massachusetts, said at the time that prosecutors supported the decision. (Tsarnaev’s defense team includes Judy Clarke, who is well-known for defending death-penalty clients such as Theodore Kaczynski, otherwise known as the Unabomber. Kaczynski pleaded guilty and avoided the death penalty.)

In the immediate aftermath of the bombing, seven in 10 Americans said they supported the death penalty for Tsarnaev. But a Boston Globe poll conducted five months after the bombing found that 57 percent of people in Massachusetts supported a life sentence, while only 33 percent wanted the death penalty for him.

Tsarnaev faces 30 charges for the bombing and for shooting and killing Sean Collier, an MIT campus police officer. Since 17 of these counts carry the potential for the death penalty, if Tsarnaev is found guilty on any one of these charges, jurors will also have to determine if he should be sentenced to death. The trial is expected to fully begin later this month and could last until May.