Mangione is accused of fatally shooting UnitedHealthcare CEO Brian Thompson outside a hotel in Midtown in December 2024.
Defence lawyers indicated on Wednesday that Mangione plans to mount a type of legal defence that allows jurors to downgrade murder charges to manslaughter if they believe a defendant lost control of their actions due to an "extreme emotional disturbance".
But allegations Mangione meticulously planned the assassination and concealed his identity as he led law enforcement on a five-day manhunt could cut against an argument that he lost control of his actions, according to former Manhattan state prosecutor Gary Galperin.
"This is a strategic choice on his part to limit his exposure on conviction, and while legally viable, I think factually he has a high hurdle to convince a jury," said Galperin, now a professor at Cardozo School of Law.
Mangione's legal team and Manhattan District Attorney Alvin Bragg's office declined to comment.
Mangione, who has pleaded not guilty to state murder, weapons and forgery charges, is expected to go to trial in September.
The brazen killing was widely condemned by public officials but became emblematic of Americans' frustration with rising healthcare costs and insurance industry practices.
An extreme emotional disturbance defence under New York law is different from an insanity defence, which requires a psychiatric diagnosis and proof a defendant did not know what they did was wrong. The emotional disturbance defence does not require a defendant to admit to the crime.
The defence has been successful in New York in cases where defendants acted with overwhelming emotions such as anger and passion or reacted to extreme trauma. The defence has been rejected in cases in which there is evidence that a defendant engaged in planning and maintained a calm, careful demeanour, according to legal experts.
Carro will decide before instructing the jury whether Mangione provided enough evidence for them to consider downgrading to manslaughter, which could spare Mangione a possible life sentence if he is convicted.
Mangione suffered from chronic back pain, according to friends and social media posts, and prosecutors say they found a notebook where he criticised the health insurance industry and wrote about "wack(ing)" an executive.
Mangione's lawyers could seek to convince jurors that the days or weeks around the alleged shooting were an extended mental health crisis that departed wildly from Mangione's normal behaviour, according to New York Law School professor Anna Cominsky.
"They could argue this isn't normally what he did: sit around and talk about how corrupt the insurance industry is," Cominsky said.
Mangione would need to show not only that he acted in a state of extreme emotional disturbance but also that there was a "reasonable explanation or excuse" for that disturbance.
Many Americans hold negative views of health insurance companies for denying claims, which could make some jurors more sympathetic to Mangione's defence. But going from hatred of insurance companies to a homicidal mental breakdown could be a bridge too far, experts said.
"Almost any one of us can relate to struggling with a health insurance company - who can't cite an example?" Galperin said.
"But then the question becomes: would it be reasonable for you to lose self-control and go out and do what he's charged with doing?"
