(CNN) Federal prosecutors Thursday urged the 1st US Circuit Court of Appeals to reject Boston Marathon bomber Dzhokhar Tsarnaev's request for an appeal, and uphold his conviction and death sentence .

Prosecutors argued that Tsarnaev's right to an impartial jury wasn't violated simply because his trial was held in Boston, not far from the deadly bombings he was convicted of playing a role in. They argue that his request for a new trial should be denied.

"Jurors who sat through the poignant trial testimony were unlikely to be influenced by any previous exposure to this media coverage," the filing states. "The mere existence of the coverage does not show that an impartial jury could not be selected in Massachusetts."

David Patton, an attorney for Tsarnaev, had no comment on the filing when contacted by CNN.

Tsarnaev's attorneys argued in late 2018 that "the community's exposure to the bombings and ensuring pretrial publicity" meant that jurors were exposed to details of the case before sitting for the trial, and were prejudiced against him.

His attorneys argue that "virtually every prospective juror had read publicity about Tsarnaev," but the government cited decisions in other similar cases that say a juror's knowledge of the facts of a case is not as important as their ability to set their opinions aside and focus on the evidence presented in court.

The government points out that jurors swore under oath that they could set aside their views if they thought Tsarnaev was guilty and simply weigh the evidence.

Defense attorneys also pointed to two jurors' social media postings using the #BostonStrong hashtag. One, Juror 286, discussed the case years before the trial. Juror 138 discussed being a part of jury selection while it was underway.

Juror 138 posted on January 5, 2015 that he was being called to jury duty, which prompted comments like, "Did you get picked for the marathon bomber trial!!!??? That's awesome!" to which he responded, "Ya awesome alright haha there's like 1000s of people."

Another friend commented, "If you're really on jury duty, this guys got no shot in hell."

The juror later posted saying, "Shud be crazy he was legit like ten feet infront of me today with his 5 or 6 team of lawyers ... can't say much else about it tho ... that's against the rules."

During jury questioning, the filing says, Juror 138 told the court, "I haven't talked to anybody about it" and lied in court when asked about his Facebook use.

On June 24, 2015, just after Tsarnaev's sentencing, Juror 138 simply posted: "Scum."

That same day, Juror 286 changed her Facebook profile picture to a "Boston Strong" banner.

The government argues that the postings do not suggest that either of the jurors were dishonest during the jury selection process, or that they harbored biases against him that they were unable to set aside.

"These Facebook posts, all of which took place after the jury rendered its verdict, do not support Tsarnaev's claim of juror bias," the government writes in its filing. "They came only after the jurors had sat through the trial and had seen the full picture of the horror that Tsarnaev caused."

Tsarnaev's defense team filed multiple motions for a change of venue before the trial, citing the heavy pretrial media coverage but were denied.

In early 2015, 1,373 jurors were summoned to the federal courthouse in Boston and given a lengthy questionnaire. Both parties involved questioned 256 of them for several weeks. Twelve jurors and six alternates were ultimately selected.

Tsarnaev, 25, is currently being held in federal prison in Florence, Colorado. He was convicted in 2015 of all 30 counts he faced, including for the deaths of Krystle Campbell, Martin Richard, Lingzi Lu and Sean Collier.

His attorneys also argued that the appeals court should vacate his death sentence because he "was just 19 years old when he committed the crimes," but prosecutors cite a Supreme Court ruling that the death penalty is allowed for anyone 18 or older at the time of their offense.