Luigi Mangione, who is accused of second-degree murder for allegedly gunning down UnitedHealthcare CEO Brian Thompson in New York City, could face additional charges, according to Manhattan District Attorney Alvin Bragg.

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 Wednesday.

“Murder 1 has a number of delineated circumstances, including, for example, a serial murder, murder of a witness, murder of a police officer,” he explained.

“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.

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.

Bragg, who has focused on cracking down on ghost guns during his time as DA, stressed, “They are lethal in the same way as a traditional gun. What is so scary about them is you can buy a 3D printer and you can print them right from your kitchen table.”

“[It’s] something we’re seeing more and more in use,” he said.

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.”

Bragg said, “We will get the defendant here and bring him to justice through our court proceeding.”

“We’re prepared to go forward,” he said. “We’re on the path to accountability and justice.”