The Biden administration is hypocritical in simultaneously imposing a moratorium on the federal death penalty and urging that the Supreme Court reinstate the death sentence for Boston Marathon bomber Dzhokhar Tsarnaev. Indeed, the administration's choice to defend capital punishment for Tsarnaev reflects the inherently arbitrary nature of death penalty decisions.

For 17 years, under both Republican and Democratic presidents, there was a hiatus in executions carried out by the federal government. The Trump administration, though, aggressively changed course and carried out 13 executions. This was more than in the previous seven decades combined. No president in more than 120 years had overseen as many executions of federal prisoners as Donald Trump.

As a candidate for president, Joe Biden said he opposed the federal death penalty. Therefore, it was no surprise when Attorney General Merrick Garland, on July 1, announced a moratorium on executions by the federal government. As Garland wrote in the moratorium memorandum, "Serious concerns have been raised about the continued use of the death penalty across the country, including arbitrariness in its application, disparate impact on people of color, and the troubling number of exonerations in capital and other serious cases."

In light of this acknowledgment, it is puzzling that the Justice Department is urging the Supreme Court to uphold the death penalty for Tsarnaev. Dzhokhar and his brother Tamerlan were responsible for the bombing at the Boston Marathon in 2013 that killed three people and injured hundreds of others. Tamerlan was killed by police, but Dzhokhar was tried for murder and sentenced to death.

The First U.S. Circuit Court of Appeals overturned his death sentence on the grounds that the trial judge had not done enough to ensure an unbiased jury in the much-publicized case and because the judge did not allow the jury to hear evidence that Tamerlan had murdered three people before the bombing. Dzhokhar had argued that he had been under the control and influence of his older brother, a violent murderer.

The appeals court did not overturn Tsarnaev's conviction, only the death sentence; under its ruling, he would have remained in prison for the rest of his life. Given Biden's opposition to capital punishment, there was no reason to seek to reinstate the death sentence.

In going to the Supreme Court, the administration had to engage in a review of the case and decide that a death sentence was appropriate for Tsarnaev, despite the appellate court's careful analysis of the serious flaws of the sentencing phase. In fact, the Justice Department, in its briefs and arguments to the Supreme Court, offered no compelling explanation of why execution is warranted in this case as opposed to other cases.

This failure goes to the heart of the problem: There is no principled way to decide when capital punishment is justified — which is why every application is inevitably arbitrary.

Justice Stephen G. Breyer has called this arbitrariness the antithesis of the rule of law. "The factors that most clearly ought to affect application of the death penalty — namely, comparative egregiousness of the crime — often do not," he wrote. "Other studies show that circumstances that ought not to affect application of the death penalty, such as race, gender, or geography, often do."

The only explanation for the Biden administration's action in the Tsarnaev case is the enormous publicity that surrounded his crime. But surely media attention cannot be the factor that determines whether capital punishment is warranted.

It is possible that the government doesn't actually intend to execute Tsarnaev even if it wins at the Supreme Court, though the government's attorney suggested otherwise at oral argument on Oct. 13.

Everything Garland said in July is exactly right: The death penalty is imposed in an arbitrary and unprincipled manner, it is disproportionately used against people of color, and there have been many instances of innocent people being wrongly convicted and sentenced to death.

Biden understands this well. Instead of defending a death sentence in court, he should end the use of the federal death penalty and commute all capital sentences to life in prison, including that of Dzhokhar Tsarnaev.

Erwin Chemerinsky is dean of the University of California, Berkeley School of Law. He is the author most recently of "Presumed Guilty: How the Supreme Court Empowered the Police and Subverted Civil Rights." He wrote this article for the Los Angeles Times.