In a recent legal development, attorneys from the Justice Department have firmly countered the defense team of Luigi Mangione, an accused assassin, by addressing a series of arguments related to his case. The defense’s challenges to the potential imposition of the death penalty have been a focal point, but federal courts have consistently rejected similar arguments over the years.

Federal prosecutors maintain that Mangione can still be afforded a fair trial despite the government’s pursuit of the death penalty. This stance was articulated in a comprehensive 144-page document titled “omnibus opposition,” which was submitted on Friday.

According to Sean Buckley, an attorney representing the federal government, the challenge of media publicity is not unprecedented in the district. He assured the judge that high-profile cases are routinely managed with effective measures to prevent any potential bias. These measures include detailed juror questionnaires regarding media exposure, individualized jury selection processes, strict instructions against media consumption, sequestration of witnesses, and specific warnings to avoid prejudice.

Luigi Mangione recently appeared in Manhattan Supreme Court for a hearing concerning the murder case against him. He stands accused of the murder of UnitedHealthcare CEO Brian Thompson, which allegedly took place on September 16, 2025.

This extensive filing was a response to the various challenges posed by Mangione’s defense in the preceding months. These challenges targeted the death penalty itself, the government’s notification of their intent to seek the death penalty, and Mangione’s federal indictment.

Buckley called some of the defense arguments premature, speculative and unsupported by evidence.

Law enforcement has methodically and purposefully trampled his constitutional rights by interrogating him without Miranda warnings in violation of the Fifth Amendment and illegally searching his property without a warrant in violation of the Fourth Amendment.

— Mangione attorney Karen Friedman Agnifilo, writing to a judge

“The defense motions have little to no chance of success, and are more to preserve the arguments and raise issues on appeal if Mangione is sentenced to death,” said Neama Rahmani, a Los Angeles trial lawyer and former federal prosecutor.

Mangione is accused in the assassination of UnitedHealthcare CEO Brian Thompson, who was shot in the back on video outside a Manhattan hotel on Dec. 4, 2024, as he walked to an investor conference that was supposed to start later that morning.

Luigi Mangione allegedly killed UnitedHealthcare CEO Brian Thompson. (AP Photo/UnitedHealth Group via AP)

Mangione faces charges in New York state and at the federal level in connection with the murder — in addition to another set of charges in Pennsylvania in connection with the fake ID and illegal handgun police say they found in his possession when they arrested him at a McDonald’s in Altoona.

But only the federal case carries the potential death penalty, and Buckley argued that the Justice Department would be acting within longstanding legal precedent in seeking it if Mangione is convicted.

“What the defendant recasts as a constitutional crisis is merely a repackaging of arguments that controlling precedent has repeatedly rejected, and none warrants dismissal of the indictment or categorical preclusion of a congressionally authorized punishment,” he wrote.

A screenshot from surveillance footage released by the NYPD shows an alleged person of interest wanted in connection with the shooting death of UnitedHealthcare CEO Brian Thompson in Midtown Manhattan on Wednesday, December 4, 2024.   (NYPD Crime Stoppers )

Mangione’s defense is fighting on multiple fronts. Earlier this year, his team succeeded in having a New York judge throw out terror charges at the state level.

In the federal case, his lawyers have asked the judge to dismiss charges of murder through use of a firearm and stalking in his federal indictment — and to have the potential death penalty taken off the table. In the New York and federal cases, they are asking the courts to suppress documents seized from his backpack during his arrest as well as statements he made before receiving a Miranda warning.

“Law enforcement has methodically and purposefully trampled his constitutional rights by interrogating him without Miranda warnings in violation of the Fifth Amendment and illegally searching his property without a warrant in violation of the Fourth Amendment,” Mangione attorney Karen Friedman Agnifilo wrote to a New York judge Tuesday.

Mangione’s lawyers have argued that the search of his belongings without a warrant during his arrest at a Pennsylvania McDonald’s was unlawful. (Southern District of New York)

Buckley countered that the defense argument against those charges is legally flawed, the backpack search would have taken place regardless, and the only pre-Miranda statement prosecutors plan to use against him is when he allegedly lied about his name in response to a question that did not require the Miranda warning.

According to court filings, one of the safety concerns officers on scene had was that there might be a bomb in the bag, which she ruled out after searching it, according to prosecutors.

“Mangione’s arrest was valid and the search of his backpack was lawful as a search incident to arrest or an inventory search,” Rahmani told Fox News Digital. “Prosecutors have the discretion to seek the death penalty and the defense arguments about pretrial publicity tainting the jury pool and double jeopardy because there are parallel state and federal prosecutions have been recycled and rejected by appellate courts for decades.”

Thompson, 50, was a father of two from Minnesota. He was visiting New York City for an investor conference at the time of his murder.

Judge Margaret Garnett has not yet ruled on Mangione’s motions.

Luigi Mangione enters the courtroom in New York City Criminal Court on Monday, December 23, 2024. Mangione was arraigned on state charges for the alleged murder of UnitedHealthcare CEO Brian Thompson. (Rashid Umar Abbasi for Fox News Digital)

She did, however, grant his request to wear civilian clothing to an upcoming hearing on the matter.

Mangione is due back in state court Monday.

“The remaining arguments are mitigation for jurors or the DOJ’s capital case review committee to consider, not something that a judge can use to strike the death penalty at this stage of the proceedings,” Rahmani said. “Bottom line is, there is no meat on the bone, but this is what defense attorneys in capital cases are expected to do to try to save their client’s life.”