WASHINGTON, Oct 13 (Reuters) - U.S. Supreme Court justices on Wednesday leaned toward reinstating convicted Boston Marathon bomber Dzhokhar Tsarnaev"s death sentence for his role in the 2013 attack that killed three people and wounded more than 260 others. The court"s conservative majority appeared sympathetic during arguments in the case toward the Justice Department"s challenge to a 2020 lower court ruling that upheld Tsarnaev"s conviction but overturned his death sentence. The three liberal justices asked tough questions of the government but it appeared unlikely that enough of their six conservative colleagues shared their concerns for Tsarnaev to prevail and secure a new trial to determine whether he should get a sentence of life in prison or death. Despite President Joe Biden"s stated goal to eliminate capital punishment at the federal level, his administration opted to carry out the appeal - initially launched by the Justice Department under his predecessor Donald Trump - of the ruling by the Boston-based 1st U.S. Circuit Court of Appeals. No federal inmates were executed for 17 years before Trump oversaw 13 executions in the last six months of his term. Biden"s attorney general, Merrick Garland, has since imposed a moratorium on federal executions. Tsarnaev"s lawyer Ginger Anders focused on whether U.S. District Judge George O"Toole, who presided over the trial, improperly excluded evidence relating to a 2011 triple murder in Waltham, Massachusetts linked to Tsarnaev"s older brother. Lawyers for Tsarnaev, who is 28 now and was 19 at the time of the attack, have argued that he played a secondary role in the marathon bombing to his brother Tamerlan, who they called "an authority figure" with "violent Islamic extremist beliefs." The conservative justices seemed willing to defer to O"Toole"s decision to exclude the evidence in part because precise details of Tamerlan"s role in the murder have not been established. The primary source of the evidence, a man named Ibragim Todashev, was killed by an FBI agent when he attacked officers during an interview. Conservative Justice Samuel Alito said if evidence of the Waltham murders were admitted, effectively a trial within a trial would be needed to determine what happened. Alito called the evidence "inadmissible many times over in a regular trial." Fellow conservative Justice Neil Gorsuch wondered what would happen if the evidence were admitted but then it is "impossible to determine who led the Waltham murders." Storm clouds roll in over the U.S. Supreme Court in Washington, U.S., September 1, 2021. REUTERS/Tom Brenner Dzhokhar Tsarnaev is pictured in this handout photo presented as evidence by the U.S. Attorney"s Office in Boston, Massachusetts on March 23, 2015. REUTERS/U.S. Attorney"s Office in Boston/Handout via Reuters/File Photo A small group of demonstrators rally against the death penalty outside the U.S. Supreme Court building, where justices were hearing arguments in the federal government"s bid to reinstate Boston Marathon bomber Dzhokhar Tsarnaev"s death sentence in Washington, U.S. October 13, 2021. REUTERS/Jonathan Ernst 1/4 Dzhokhar Tsarnaev is pictured in this handout photo presented as evidence by the U.S. Attorney"s Office in Boston, Massachusetts on March 23, 2015. REUTERS/U.S. Attorney"s Office in Boston/Handout via Reuters/File Photo Read More Liberal Justice Elena Kagan said Tsarnaev"s lawyers are desperate to introduce mitigating evidence showing their client was in thrall to his brother. O"Toole allowed some evidence about the brothers" relationship, but stopped short of "evidence of a gruesome, murderous crime" that would illustrate the "extraordinary influence" of the older brother over other people, Kagan added. Fellow liberal Justices Stephen Breyer and Sonia Sotomayor seemed to share Kagan"s view. Chief Justice John Roberts was the only one of the court"s conservatives who indicated he potentially could side with Tsarnaev on the Waltham murders issue. Roberts said it should be easier to admit evidence during a proceeding that would determine whether someone is sentenced to death than for other reasons. The 1st Circuit also found that O"Toole "fell short" in screening jurors for potential bias following pervasive news coverage of the bombings. There was little discussion of that issue during Wednesday"s argument. Tsarnaev"s lawyers have said O"Toole"s decisions deprived him of his constitutional right to a fair trial and violated a U.S. statute that outlines the procedure for imposing the death penalty under federal law. "END GAME" Asked by conservative Justice Amy Coney Barrett what the government"s "end game" is regarding Tsarnaev"s execution in light of Garland"s moratorium, Deputy Solicitor General Eric Feigin said the Biden administration believes the jury reached a "sound verdict and that the court of appeals was wrong to upset that verdict." The Tsarnaev brothers detonated two homemade pressure-cooker bombs at the marathon"s finish line on April 15, 2013, and days later killed a police officer. Tamerlan Tsarnaev died after a gunfight with police. Jurors convicted Dzhokhar Tsarnaev on all 30 counts he faced and determined he deserved execution for a bomb he planted that killed Martin Richard, 8, and Chinese exchange student Lingzi Lu, 23. Restaurant manager Krystle Campbell, 29, was killed by the second bomb. Reporting by Lawrence Hurley in Washington and Nate Raymond in Boston; Editing by Will Dunham and Scott Malone