The ghost gun allegedly in Luigi Mangione's possession when he was arrested has been matched to three shell casings recovered at the crime scene in New York.

Luigi Mangione, 26, is accused of killing UnitedHealthcare CEO Brian Thompson.

The ghost gun allegedly in Luigi Mangione's possession in Pennsylvania was matched to three shell chasings recovered in New York, according to police commissioner Jessica Tisch.

Luigi Mangione refused to waive extradition from Pennsylvania to New York where he is charged with murdering UnitedHealthcare CEO Brian Thompson.

Thomas Dickey, the defense attorney for Mangione, who is accused of killing Brian Thompson, discusses his client’s refusal to waive extradition to New York and concerns over evidence in the case.

Video captured the moment the gunman walked up behind the CEO outside the Hilton in Midtown Manhattan, pointed his gun at him and fired.

Luigi Mangione appeared to frequently discuss what he claimed were his health troubles -- including back pain, brain fog, and sciatica -- online.

Before he was arrested Luigi Mangione walked into the Horseshoe Curve Lodge in Altoona, Pennsylvania, one morning looking for a room, according to the desk clerk.

Luigi Mangione appeared to frequently discuss what he claimed were his health troubles -- including back pain, brain fog, and sciatica -- online.

Luigi Mangione yelled to the press about "an insult to the intelligence of the American people" as he was physically dragged into a Pennsylvania courthouse.

The bulletin warned that Thompson's killing may be used as "messaging and propaganda" to share the techniques and tactics for targeting other health care companies.

Online posts have listed the names and salaries of health insurance executives and "Wanted" signs have been posted in Manhattan, according to the bulletin.

Luigi Mangione may have found inspiration in Ted Kaczynski, police intel says.

The firearm found on the suspect in the murder of the UnitedHealthcare CEO is believed to have been an untraceable ghost gun, according to police.

The suspect in the shooting of the United Healthcare CEO had several handwritten pages on him that indicated frustration with the health care system, a detective said.

Luigi Mangione was taken into custody in Pennsylvania on Monday following a dayslong manhunt for the suspect in the fatal shooting of UnitedHealthcare CEO Brian Thompson.

UnitedHealthcare CEO shooting suspect Luigi Mangione has arrived at his extradition hearing, shouting at gathered press outside of the Pennsylvania courtroom.

White House press secretary Karine Jean-Pierre addressed the UnitedHealthcare CEO shooting and sent condolences to the victim's family.

Former FBI agent Brad Garrett discusses the investigation into Luigi Mangione, the suspect arrested in connection to the shooting of UnitedHealthcare CEO Brian Thompson.

The man charged with murder for gunning down UnitedHealthcare CEO Brian Thompson was arrested and charged after the shooting outside a Hilton Hotel in Midtown Manhattan.

Mangione is a May 2020 graduate of the University of Pennsylvania, according to a school spokesperson. He earned bachelor's and master's degrees in engineering from the Ivy League institution.

Jessica Tisch and Joseph Kenney join "GMA" to discuss the investigation and charges facing suspect Luigi Mangione in the shooting of UnitedHealthcare CEO Brian Thompson.

Luigi Mangione was arrested at a McDonald’s in Pennsylvania, after he was recognized from surveillance images, and is facing a second-degree murder charge in New York in the death of Brian Thompson.

The NYPD filed second-degree murder charges against Luigi Mangione, the suspected shooter of UnitedHealthcare CEO Brian Thompson, according to an online court docket.

The suspect charged in the fatal shooting of UnitedHealthcare CEO Brian Thompson was arrested in Altoona, Pennsylvania.

Luigi Mangione was arrested by Pennsylvania police on unrelated charges, authorities said. The 26-year-old is in custody as a suspect in connection with Brian Thompson's murder.

Luigi Mangione is in custody in Altoona, Pennsylvania, as a person of interest in the murder of UnitedHealthcare CEO Brian Thompson in New York City last week, according to authorities.

Luigi Mangione, who was arrested in Altoona, Pennsylvania, is a suspect in the murder of UnitedHealthcare CEO Brian Thompson, police said.

Police are questioning the 26-year-old in Altoona, Pennsylvania, in connection with the murder of UnitedHealthcare CEO Brian Thompson last week, according to multiple law enforcement officials.

Monday's arrest in the high-profile killing of UnitedHealthCare CEO Brian Thompson in the heart of New York City boiled down to "good old-fashion police work," authorities said.

New video obtained by ABC News shows UnitedHealthcare CEO Brian Thompson's killer waiting for him moments before last week's shooting in Midtown Manhattan.

A man in Pennsylvania is being held for questioning in connection with the murder of UnitedHealthcare CEO Brian Thompson in New York City, law enforcement sources told ABC News.

The manhunt for the suspect who killed UnitedHealthcare CEO Brian Thompson has now entered its fourth day as authorities learn more about his movements before the attack.

NYPD detectives arrived in Atlanta on Saturday as they probed leads in the shooting of UnitedHealthcare CEO Brian Thompson in New York.

ABC News’ Aaron Katersky and former FBI agent Brad Garrett discuss the latest in the investigation related to the murder of UnitedHealthcare CEO Brian Thompson.

The NYPD is hoping someone recognizes the latest images of the suspected shooter of UnitedHealthcare CEO Brian Thompson.

Images of the suspect appear to show him on the day of the shooting of United Healthcare CEO, Brian Thompson.

The Atlanta Police Department confirmed the arrival of the New York team but declined to give more specifics.

Psychiatrist and author Dr. Judith Joseph joins ABC News Live to discuss the reaction on social media to the killing of UnitedHealthcare's CEO.

ABC News contributor Brad Garrett joins Live to discuss updates in the shooting of UnitedHealthcare CEO Brian Thompson.

ABC News’ Aaron Katersky reports on killing of the UnitedHealthcare CEO on “This Week”

ABC News’ Martha Raddatz speaks with Bob Boyce and Mary O’Toole on “This Week.”

New York Police Department detectives arrived in Atlanta, Georgia, on Saturday following a large number of tips linked to the UnitedHealthcare CEO murder suspect.

Retired NYPD detective and director of the Black Law Enforcement Alliance Marq Claxton details his thoughts on the investigation process and the new evidence broadening the search for the gunman.

As the manhunt enters its fourth day, the FBI is now offering a $50,000 reward in the search for the suspected gunman who killed the CEO of UnitedHealth.

Police say the suspect in the ambush of CEO Brian Thompson earlier this week likely took a bus out of the city, but left his backpack behind. The FBI now joins in his nationwide search.

Fury, anger and resentment toward the health care industry have exploded in the public rhetoric in the wake of United Health Care CEO Brian Thompson's murder.

The FBI has joined the nation-wide search for the gunman in the fatal shooting of UnitedHealthcare CEO Brian Thompson.

The unidentified man suspected of gunning down UnitedHealthcare CEO Brian Thompson outside a Midtown Manhattan hotel remains at large after Wednesday's attack.

Investigators said the suspect in Wednesday's deadly shooting seems to have escaped via the George Washington Bridge bus station. Officers also found what they believe is the suspect's backpack.