Authorities are questioning Luigi Mangione, 26, as a person of interest in connection with last week's shooting of UnitedHealthcare CEO Brian Thompson.
Detectives in Altoona, Pennsylvania picked him up after a McDonald's employee thought it might be the suspect.
Mangione was allegedly found to have a firearm similar to the one used in the shooting. It was described as a ghost gun that could fire a 9mm bullet. Police say it may have been created using a 3D printer.
The NYPD said he had a gun suppressor and several fake IDs on him.
He was also carrying a 3-page manifesto that "speaks to motivation and mindset," police said.
It reportedly showed he harbored "ill will" to corporate America.
Thompson, 50, was in New York City for the company's annual investors meeting last Wednesday when he was ambushed by a masked shooter who fired off several rounds into his back and leg, leaving him mortally wounded.
The killer then fled – first on foot, then by e-bike. He subsequently boarded a bus departing New York City, leaving authorities to believe he was no longer in the area.
Preliminary evidence indicated Thompson's murder was a "premeditated, pre-planned, targeted attack," NYPD Commissioner Jessica Tisch, who confirmed the suspect was "lying in wait" for at least five minutes before he approached the victim, told reporters at a press conference.
At the crime scene, investigators recovered live 9mm rounds and three discharged casings engraved with words "deny," "depose," and "defend." The words appear to allude to the title of Jay Feinman's book "Delay, Deny, Defend," which criticizes the practices of insurance companies.
Last week, police released surveillance images of the shooter with his face mask pulled down, smiling and flirting with a female front desk worker as he used a fake New Jersey ID to check into the HI New York City Hostel prior to carrying out the deadly incident.
The assassin, who is believed to have arrived in NYC 10 days before the shooting, was also spotted at a nearby Starbucks that same day.
Over the weekend, police released two new photos of the masked suspect appearing in the back of a taxi.
A $10,000 reward was being offered to anyone with information leading to an arrest and conviction.
A motive remains under investigation.
