In his first comments since Luigi Mangione was charged with second-degree murder on Monday, Manhattan District Attorney Alvin Bragg said he was confident that the 26-year-old would quickly be extradited to New York where he will be held accountable for brazenly gunning down UnitedHealthcare CEO Brian Thompson.

"We will get the defendant here and bring him to justice through our court proceeding," Bragg told ABC News on Wednesday, saying that Mangione could face additional charges beyond the second-degree murder charges he currently faces.

"As we learn more about motives and other things like that ... there may be additional charges," Bragg said.

Mangione is also charged in New York with criminal possession of a forged instrument and several counts of criminal possession of a weapon.

"We intend to learn more, and we have a lot of things to do," Bragg said. "As things go forward, there may be additional charges to bring," Bragg said.

Mangione's attorney, Thomas Dickey, said his client intends to plead not guilty to the charges, claiming there is no evidence linking his client to the crime. Bragg said he was confident Mangione is the person who fired three rounds into the torso of Thompson last week, killing the health care executive and setting off a firestorm of vitriol online.

"We would not charge the person if we didn't think it was the person, and we're prepared to go forward and we're on the path to accountability and justice," Bragg said.

Once the former Ivy Leaguer is extradited to New York, Bragg said Mangione will face a team of Manhattan's most seasoned homicide prosecutors. The DA acknowledged that the nature of the alleged crime is "extraordinarily scary."

"It is very scary, and it is something that has the attention of so many who live here, so many who come to work here, and rightfully so," Bragg said.

Bragg's comments come the same day that the New York Police Department offered the first forensic evidence linking Mangione to the alleged crime. According to Police Commissioner Jessica Tisch, fingerprints from the crime scene have been matched to Mangione, and three shell casings recovered following the midtown shooting were matched to Mangione's 3D-printed handgun. Bragg's office said his office has focused on combating so-called ghost guns since the beginning of his tenure as district attorney.

"It's something we're seeing more and more in use, speaking generally. It's something also we've seen people who are younger and younger working on," Bragg said.

Asked why Mangione was charged with second-degree murder, Bragg told ABC News that prosecutors wanted to bring charges quickly and first-degree murder "has a number of delineated circumstances."

"Murder 2 is the intentional killing of a person, punishable by 25 years to life under New York law," Bragg said. "Murder 1 has a number of delineated circumstances, including, for example, a serial murder, murder of a witness, murder of a police officer."

Bragg has found himself at the center of multiple high-profile cases -- including his conviction of former President Donald Trump and recent acquittal of Marine veteran Daniel Penny. With the Mangione case, Bragg is expected to face not only a high-profile prosecution but also a groundswell of public support for the accused murderer,.

"I ... have spent time with families of homicide victims with survivors of violent crime," Bragg said. "That's the centerpiece of our work, and to think that there are others celebrating this conduct is beyond comprehension to me."

Mangione, a 26-year-old Ivy League graduate, is accused of shooting Thompson outside a Midtown Manhattan hotel on Dec. 4 while the CEO was heading to an investors conference.

Thompson's murder ignited online anger at the health insurance industry and some people online have celebrated the suspect.

"Celebrating murder is abhorrent," Bragg said. "I sit across the table from families who've had a loved one killed. And to think of people celebrating that ... is beyond comprehension to me."

"What I would say to members of the public ... [who are] celebrating this and maybe contemplating other action: We will be vigilant and we will hold people accountable," Bragg said.

The ghost gun allegedly in Mangione's possession when he was arrested has been matched to three shell casings recovered at the murder scene, according to the NYPD.

Fingerprints recovered from a water bottle and a Kind bar near the crime scene have also been matched to Mangione, police said.

Mangione was apprehended in Altoona, Pennsylvania, on Monday after nearly one week on the run. He's also facing charges in Pennsylvania, including allegedly possessing an untraceable ghost gun.

Mangione plans to challenge his extradition to New York.

The Manhattan District Attorney's Office said it will seek a governor's warrant to try to force Mangione's extradition. New York Gov. Kathy Hochul said in a statement that she'll sign a request for the governor's warrant "to ensure this individual is tried and held accountable."