In a 6-3 decision last week, the US Supreme Court reinstated the death penalty for Boston Marathon bomber Dzhokhar Tsarnaev. Reversing a First Circuit Court of Appeals ruling that had voided the sentence, the justices concluded that Tsarnaev had been fairly tried by an impartial jury and that the punishment imposed by the trial court was appropriate.

Now that the highest court in the land has disposed of the last legal objections in the case, there is no reason to delay Tsarnaev’s punishment any further. For his role in committing one of the worst horrors in Boston’s history, the federal government is duty-bound to put Tsarnaev to death. It should proceed to do so, and bring this awful chapter to a close.

At every step of the way, to its great credit, the federal government has been unflagging in its resolve to make Tsarnaev pay the ultimate price for his crimes.

It was the federal government, under then-president Barack Obama and his attorney general, Eric Holder, that prosecuted Tsarnaev for his role in the Marathon bombing, indicting him on 30 charges, 17 of them capital offenses.

It was the federal government that made the decision in 2014 to seek the death penalty for Tsarnaev in light of the “heinous, cruel, and depraved manner” in which he perpetrated his atrocities.

It was the federal government, under President Biden and Attorney General Merrick Garland, that last summer turned to the Supreme Court after the Appeals Court threw out Tsarnaev’s death sentence, urging the justices to take up the matter and “put this case back on track toward a just conclusion.”

And it was the federal government, represented by Deputy Solicitor General Eric Feigin, that told the high court in October that — notwithstanding the administration’s opposition to capital punishment as a matter of policy — it believed that “the jury imposed a sound verdict and that the court of appeals was wrong to upset that verdict.”

The administration’s argument prevailed. The terrorist who murdered Krystle Campbell, Lingzi Lu, Martin Richard, and Sean Collier was condemned to death under the laws of the land. That sentence has been fully litigated and upheld on appeal. Regardless of Biden’s (current) views on capital punishment, his legal duty is clear. Under Article II, Section 3 of the Constitution, he is obliged to “take Care that the Laws be faithfully executed.” He must fulfill that obligation by proceeding now to carry out Tsarnaev’s punishment.

The Biden administration has declared a “moratorium” on executions pending a Justice Department “review” of policies and procedures. But an informal moratorium does not override a judgment duly rendered in a court of law and affirmed by the Supreme Court. The judge and jurors reached a verdict, and that verdict was upheld on appeal. Now the job of the executive branch, regardless of the political views of the president or anyone else, is to see to it that the judgment is implemented. That is what it means to live under a government of laws. Once the courts have settled the question of what justice and the law require, the executive departments comply — regardless of whether they agree or disagree. And if that’s the case when the courts rule against the executive branch, how much more so is it the case when, as here, they rule in the government’s favor?

The federal death penalty is meant to be reserved for the very worst of American criminals. On April 15, 2013, Tsarnaev, working with his older brother, Tamerlan (who was killed several days later), deposited a pressure-cooker bomb filled with explosives, nails, and metal shards a few inches behind a small boy in the midst of a crowd of joyful Marathon spectators. Then he sauntered away and detonated his bomb, turning Copley Square into a scene of what the Court of Appeals called “battlefield-like carnage,” in which “blood and body parts were everywhere.” That little boy and two young women were gruesomely murdered; more than 260 other people were injured, many of them maimed for life.

If anyone qualifies as worst of the worst, Tsarnaev does. If anyone merits the worst punishment in our legal system, Tsarnaev does. Indeed, for crimes like his, any lesser punishment would be a miscarriage of justice. Granted, not all Americans share that view. But what justice requires isn’t determined by popular vote. It is determined through due process of law: an impartial judge and jury, a fair trial, elaborate protections for the accused, and the right of appeal.

All of that Tsarnaev received. Now he should get the punishment he deserves, and be put to death.

(Jeff Jacoby is a columnist for The Boston Globe).