The most serious charge against the man accused of killing the UnitedHealthcare CEO in broad daylight last week on a Manhattan sidewalk is murder in the second degree.

Given the image of the homicide captured on surveillance video – a dark-hooded figure with a gray backpack fatally shooting the executive in the back from several feet away – the case may seem like an obvious candidate for an even more severe charge.

But under New York law, a first-degree murder charge only applies to a narrow list of aggravating circumstances, including when the victim is a judge, a police officer or a first responder, or when the killing involves a murder-for-hire or an intent to commit terrorism, legal experts told CNN.

While state prosecutors have not tipped their hand on precisely what evidence they’re leaning on as they seek an indictment against Luigi Mangione, it’s possible details emerge that could allow them to upgrade the second-degree murder charge, legal experts told CNN.

A charge of first-degree murder would raise the case’s already sky-high profile while also reducing the possibility defense lawyers could argue down the second-degree murder charge to an even lesser one with a much lighter maximum sentence.

Stiffer penalties also could be in play if federal prosecutors opt to charge Mangione in the case, legal experts said, possibly over interstate travel law enforcement officials have described as part of the alleged plot to kill CEO Brian Thompson.

Terrorism proof could be key to an upgraded charge in the case

If it appears, for instance, the suspect had planned the killing for a while, evidence may point to a terrorism angle that could merit a bump-up to a first-degree murder charge in New York, said David Shapiro, a lecturer at the John Jay College of Criminal Justice.

“Terrorism is defined, basically, as creating, intimidating the civilian population or influencing a government unit to act in a certain way,” Shapiro told CNN. “You can easily imagine a set of facts where Mangione was attempting to do the same or did the same. I’m sure there are a host of insurance company executives that are afraid of copycats.”

Mangione, 26, appeared to be driven by anger against the health insurance industry and against “corporate greed” as a whole, according to a New York Police Department intelligence report obtained this week by CNN.

“He appeared to view the targeted killing of the company’s highest-ranking representative as a symbolic takedown and a direct challenge to its alleged corruption and ‘power games,’ asserting in his note he is the ‘first to face it with such brutal honesty,’” says the NYPD assessment based on a handwritten “claim of responsibility” Mangione had when he was arrested and his prior social media posts.

Indeed, the killing of Thompson, a husband and father of two, has laid bare many Americans’ fury toward the health care industry and struck fear in C-suites across the country, with the NYPD intel report warning online rhetoric could “signal an elevated threat facing executives in the near-term … ”

That Mangione was arrested Monday in Pennsylvania with a 3D-printed gun, fake IDs and the three-page “claim” – which indicated no specific threats but only “ill will towards corporate America,” the NYPD’s chief detective has said – further shows he might have been planning more attacks, Shapiro said.

“Why would you want to carry all that incriminating evidence of what you just did?” he said. “Maybe it’s not that he’s stupid but he’s planning to use this stuff again.”

The gun taken from Mangione upon arrest matches three shell casings found at the crime scene and marked with “deny,” “defend” and “depose” – words similar to those used in, as well as to criticize, insurance industry practices – top NYPD officials said this week. Mangione’s fingerprints match those on items he was captured on surveillance video buying shortly before the homicide and found after it nearby, the police commissioner added.

Mangione’s lawyer anticipates he will plead not guilty to the murder charge and four other charges in New York, as well as to charges related to the gun and ID in Pennsylvania, he said. Attorney Thomas Dickey hadn’t “seen any evidence that they have the right guy,” he said Tuesday, adding New York officials “need to convince me.”

Mangione has been denied bail in Pennsylvania and is fighting extradition to New York.

2nd-degree murder charge has a key caveat

If convicted of second-degree murder in New York, Mangione would face 15 years to life in prison, while a first-degree murder charge carries a sentence of 20 years to life.

But a second-degree murder charge in New York also includes a key option a first-degree murder charge does not: It allows the defendant an “affirmative defense,” essentially a “Yes, but” argument that could lessen the seriousness of the charge to first-degree manslaughter, Shapiro said.

And in New York, a first-degree manslaughter charge carries a maximum sentence of 25 years in prison – substantially less than either of the murder charges.

It’s also possible Mangione’s alleged actions could become the target of federal prosecutors if he traveled across state lines to commit an act of violence, said Elie Honig, a CNN senior legal analyst and former federal and state prosecutor.

Mangione got to New York days before Thompson’s killing via a Greyhound bus that originated in Atlanta, law enforcement sources have told CNN.

Federal prosecutors would have to decide whether charges are necessary or redundant, including whether a defendant is charged with the same crime in another jurisdiction, Honig said.

Federal statutes carry much more serious penalties – mandatory life imprisonment up to and including the death penalty, which New York does not have.

Why Mangione may be fighting extradition

Mangione, meanwhile, is fighting extradition from Pennsylvania, where a tip led police to him this week at a McDonald’s in Altoona.

Staying put would give the suspect more time to consider his defense, demand prosecutors present more evidence or, however unlikely, try to get bail in Pennsylvania, CNN Legal Analyst Karen Agnifilo said.

“Eight or 9 out of 10 times, defendants waive extradition because they realize this is so perfunctory, it’s so easy, and most of them don’t want to languish in detention in the other state because you don’t even get to fight your case yet,” said Agnifilo, who previously worked at the Manhattan District Attorney’s Office.

But in murder cases like Mangione’s, she said, “there’s no chance he’s going to be let out, so he’s fighting extradition.”

While it could take up to two months for authorities to get Mangione to New York, prosecutors there will begin testing forensic evidence, reviewing DNA results and scouring video footage to put together a timeline to show a jury “almost a movie of his movements to successfully conclude that this is in fact the same person responsible for this crime,” the NYPD’s former Chief of Department Ken Corey told CNN.

Resolving extradition then sets the stage for Mangione to enter a plea and investigators to start producing evidence and discovery, said Shapiro, who expects the process to be resolved within 30 days, given the case’s high-profile nature.

This story has been updated with additional information.

CNN’s Dalia Faheid, Michelle Watson, John Miller and Dakin Andone contributed to this report.