How investigators are building a case against alleged CEO killer Luigi Mangione based on a trail of evidence

A moment of levity and a desire for a quick drink and a bite to eat.

Those were the mistakes suspected CEO killer Luigi Mangione made, resulting in his arrest in the fatal shooting of UnitedHealthcare executive Brian Thompson in midtown Manhattan on Dec. 4, multiple law enforcement experts say.

“I don’t think anywhere in his planning was ‘I want to get a Kind bar,’ or I’m gonna go to a hostel and flirt with a girl,” said David Sarni, a retired NYPD detective on the job for 27 years and a current adjunct professor at John Jay College of Criminal Justice in Manhattan. “Those are things you do as a human being. People make mistakes and detectives are going to exploit those mistakes.”

Investigators work the clues

Those apparent errors police said have provided fingerprint matches to Mangione, as well as a ballistics match between shell casings found at the scene and a firearm Mangione was carrying at the time of his arrest, will be key pieces of evidence police and prosecutors will use to build their murder case against the 26-year-old computer engineer from Towson, Maryland.

Despite what appears to have been extensive planning and preparation to carry out the killing, several actions — like pulling down his mask, dropping a water bottle and snack wrapper, for example — have helped detectives tie Mangione, who came from a prominent Maryland family, to the killing.

Mangione had, until just before his arrest on Monday, managed to fly under the radar.

NYPD Chief of Detectives Joseph Kenny said investigators didn’t have a suspect’s name until Mangione stopped for a meal at McDonald’s, indicating Mangione could have potentially continued to evade authorities.

Nor did authorities have a potential motive for the killing

Investigators are examining whether Mangione, who was high school valedictorian at his elite prep school in Maryland and went on to earn two degrees from the University of Pennsylvania, was moved to allegedly kill Thompson, a married father of two from Minnesota, after he suffered a back injury and was dissatisfied with the results and his interactions with the health insurance industry, a police official said. On Thursday, police officials said Mangione did not appear to be a client of the insurance company, and that he had knowledge of the investors meeting that took Thompson to New York for months before the shooting.

An alleged manifesto

After his arrest, police found a three-page “manifesto,” in which Mangione apparently voiced disdain for the nation’s health care systems.

Another passage included: “To the Feds, I’ll keep this short, because I do respect what you do for our country. To save you a lengthy investigation, I state plainly that I wasn’t working with anyone,” The Associated Press reported the document said. “I do apologize for any strife or traumas but it had to be done. Frankly, these parasites simply had it coming.”

The New York Times reported that handwritten words in a spiral notebook found with Mangione stated: “What do you do? You wack the CEO at the annual parasitic bean-counter convention. It’s targeted, precise, and doesn’t risk innocents.”

Defense attorney Jeffrey Lichtman, of Manhattan, who isn’t involved in the case, believes that Mangione’s legal team should move to mount a defense based on what he said were Mangione’s apparent emotional issues, which he said would be their best shot at reducing the murder charge.

“Extreme emotional disturbance is the defense to knock down the murder charge to manslaughter in the first degree,” said Lichtman, referring to the affirmative defense that Mangione’s attorneys would have the burden of proving.

The so-called manifesto found among Mangione’s possessions when he was arrested Monday morning in Altoona, Pennsylvania indicates that he was “completely out there” in terms of his mental state, Lichtman said.

Based on the trove of evidence against Mangione that the NYPD has amassed, Lichtman said “my gut tells me this is not a case where they can say he was not the shooter.”

Mangione shouted toward television cameras as he was being brought into a Pennsylvania courthouse after his arrest, saying that something, which was inaudible, was “clearly out of touch and an insult to the intelligence of the American people.”

Professor David Shapiro, of John Jay College of Criminal Justice, said the extreme emotional disturbance defense could be a possibility for Mangione’s defense, and agreed that the evidence that authorities have described thus far is “devastating stuff, devastating stuff.”

A missing persons report

Mangione’s mother had reportedly filed a missing persons report with San Francisco police in November after not hearing from Mangione, who had previously lived in that California city as well as Honolulu, Hawaii, in several months, according to multiple news reports.

For now, Mangione remains in a Pennsylvania prison, held without bail on weapons and forgery charges after he was found with several fake IDs — including what police said was the same New Jersey driver’s license used to check into an Upper West Side hostel where police said the gunman stayed before the shooting outside the New York Hilton on Sixth Avenue — and a 3D-printed illegal ghost gun, which authorities said appears to be the same gun that fired the bullets that struck Thompson, based on NYPD ballistics testing.

Peter J. Weeks, the district attorney in Blair County, Pennsylvania, said in an email to Newsday: “The defendant was given 14 days by the Court to file a formal motion contesting extradition. The Commonwealth has 30 days to obtain a Governor’s warrant to effectuate the extradition. I expect the Court will schedule a hearing to occur sometime after the 14 day deadline.”

Defense says there is “no evidence” against Mangione

Manhattan prosecutors have charged Mangione with second-degree murder and other charges in the Dec. 4 killing of Thompson. He’ll be arraigned on those charges once he has been returned to New York. Weeks has said he’ll allow New York to prosecute Mangione first, but said he plans to eventually press forward with his case, too.

Mangione’s Pennsylvania-based defense attorney Thomas Dickey, has not responded to message seeking comment, but has said in nationally televised interviews that his client intends to plead not guilty to the charges in both New York and Pennsylvania. Dickey has said he has seen “no evidence” linking his client to the crimes for which he’s been charged.

Meanwhile, with a suspect in custody, NYPD officials said they are attempting to construct a definitive timeline of the events surrounding and including the shooting, focusing on Mangione’s actions before and after the killing to establish motive and to place him as close as possible to the shooting itself.

The idea, said retired NYPD detective Joseph Giacalone, who has been an adjunct professor at John Jay, is to place Mangione as close as possible to the shooting, even if there is no actual eyewitness who can testify that he was seen pulling the trigger. The suspected gunman wore a face mask and hooded jacket — preventing any eyewitnesses from being able to positively identify the shooter — according to video footage of the shooting released by the NYPD.

Legal experts agree that the case as it currently stands against Mangione is largely circumstantial, but Giacalone thinks the NYPD will have no trouble pulling together a compelling narrative for a jury of Mangione’s peers, which will include key clips of video surveillance, culled from hours of footage.

“They will put him there,” said Giacalone, referring to Mangione’s proximity to the shooting.

A face and a smile

A major break in the investigation came when a man who police believe is Mangione, apparently while flirting with a clerk at the Upper West Side hostel where police said he stayed in the days leading up to the killing, removed his face mask and flashed a smile.

Police shared that photograph online and to the news media, which helped a customer in a McDonald’s nearly 300 miles away from New York City recognize a fellow customer — later identified as Mangione — munching on a hash brown on Monday morning.

Part of the reason Mangione was also able to avoid arrest in the immediate days after Thompson’s assassination: He had no prior criminal record.

Therefore, his DNA and fingerprints weren’t in the databases containing that information on individuals who have been previously convicted of crimes, which are frequently used by law enforcement, officials said.

But after his arrest, according to NYPD Commissioner Jessica Tisch, the department’s crime laboratory in Queens was able to link Mangione to the crime scene through his fingerprints on a water bottle and Kind bar wrapper that were found near the scene of the shooting.

Also, ballistics testing done at the crime lab confirmed that the illegal ghost gun — built with the help of a 3D printer and without a serial number to trace it — Mangione was carrying at the time of his arrest, was determined to have been the same gun that fired the rounds at Thompson, Tisch said.

A message at the crime scene

The three shell casings found at the scene had a message for investigators, a police official has said, with the words “delay,” “deny” and “depose” printed on the shell casings, a law enforcement source has told Newsday, another possible indication of a motive.

Those words are similar to a 2010 book entitled “Delay, Deny, Defend: Why Insurance Companies Don’t Pay Claims and What You Can Do About It” by Jay M. Feinman, a professor at Rutgers Law School.

Investigators still have plenty of work to do. Detectives need to trace Mangione’s steps after the killing and work to access his digital footprint, including his electronic devices, Sarni said.

One question that apparently hasn’t been answered is how the suspected shooter knew where to be in order to encounter Thompson at 6:44 a.m. outside of a massive hotel with multiple entrances and exits? Or was it just a morbid stroke of luck?

“How did he know to be at the scene at the time he was there?” Sarni said. “Hopefully, what he wrote will help them figure that out.”