A lawyer for Luigi Mangione, the man accused of fatally gunning down U.S. health insurance executive Brian Thompson in December, told a judge Friday (February 21) that her client was illegally searched during his arrest and she would seek to exclude that evidence from his trial on state murder and terrorism charges.

Lawyer Karen Agnifilo said during a hearing in Manhattan state court that there were "serious search and seizure issues" with Mangione's December arrest in Pennsylvania, though she did not elaborate.

"There might be evidence that is suppressed in this case," Agnifilo said.

READ: Suspect in health CEO killing charged with murder in New York

Police officers in Altoona, Pennsylvania, found Mangione with a 9-millimeter pistol and silencer, clothing that matched the apparel worn by Thompson's shooter in surveillance footage, and a notebook describing an intent to "wack" an insurance company CEO, according to a court filing.

Thompson, the former CEO of UnitedHealth Group's insurance unit UnitedHealthcare, was shot dead on December 4 outside a Midtown Manhattan hotel, where the company was gathering for an investor conference.

Mangione, 26, appeared in court wearing a green cable knit sweater over a white shirt. He was brought into the courtroom in leg and arm shackles and wearing a bulletproof vest.

Mangione pleaded not guilty on December 23 to an 11-count indictment charging him with murder as an act of terrorism and weapons offenses.

If convicted, Mangione could face life in prison without parole. He is now jailed in a federal lockup in Brooklyn.

The Friday hearing was brief and largely concerned prosecutors' progress in handing over evidence to Mangione’s legal team.

The brazen killing of Thompson and ensuing five-day manhunt captivated Americans.

While public officials condemned the killing, some Americans who decry steep healthcare costs and insurers' power to refuse to pay for some treatments have feted Mangione as a folk hero.

Dozens of Mangione supporters gathered outside the courthouse on Friday and behind police barricades in the hall outside the courtroom.

Protesters across the street from the courthouse held signs reading "FREE LUIGI" and chanting in unison, "Free, free Luigi!" and "Stop denials with AI! How many people have to die?!"

Gladys Sharpp, a home health aid from Long Island, New York, voiced her support for Mangione.

"I am here with my friends because we support Luigi Mangione for unaliving CEO Brian Thompson. We are taking a stand, and most of the world as well, is tired of insurance companies being corrupt and denying people hundreds of coverages. We are hoping that he walks a free man today," she said.

Bo Dittle, a 22-year-old visitor from Nashville, Tennessee, disagreed.

"I think that murder is always wrong," he said. "And it's kind of sickening that they're trying to condone or advocate for a murder when just because he's attractive and they killed someone that they don't like. Murder is never the answer."

Mangione also faces a four-count federal criminal complaint charging him with stalking and killing Thompson.

Agnifilo said prosecutors overseeing that case are weighing whether to seek the death penalty, which she said was complicated by the slow pace of discovery in the state case.

Mangione has not yet entered a plea in the federal case.

Avraham Moskowitz, a lawyer with experience in death penalty cases, joined Mangione's defense team this month.

(Production: Justin Nathanson, Roselle Chen)