As the investigation into the fatal shooting of a health care executive in Manhattan enters its fifth day, police are missing key pieces of evidence and are combing through what they have gathered for more clues, as the suspect remains on the run.

The New York Police Department is getting help from the FBI and other law enforcement agencies across the country to search for the suspect, with the public being encouraged with rewards. Two new photos released by police show the suspect masked with a hood in the backseat of a vehicle and wearing a jacket walking on the street.

While authorities say they believe the suspect has long left New York City after fatally shooting UnitedHealthcare CEO Brian Thompson on Wednesday, officials said they feel confident he will be captured.

“Let him continue to believe he can hide behind a mask,” New York City Mayor Eric Adams said of the suspect. “We’re going to reveal who he is, and we’re going to bring him to justice.”

Here’s what authorities are still trying to find:

And here are some of the key pieces of evidence they’ve gathered:

But crucially, there was no gun in the backpack.

That sent investigators back to the park. On Saturday, police divers searched a body of water known as the Lake, in an area of Terrace Drive near the park’s iconic boathouse and Bethesda Fountain, a law enforcement official said.

After recovering the Peak Design backpack from Central Park on Friday, police examined it at a forensic lab in Queens. Inside, they found Monopoly money, a law enforcement source told CNN. It also contained a Tommy Hilfiger jacket, and it was not immediately clear if other items were in the backpack, officials said.

There has still been no sign of the bicycle.

Meanwhile, photos of the suspect have been circulated to multiple law enforcement agencies, including airports and border patrol stations along the Mexican and Canadian borders in the hope he won’t slip out of the country.

The FBI is offering up to $50,000 of reward money for information leading to his arrest and conviction. The NYPD has added another $10,000.

Piecing together clues

The search for the suspect and more physical evidence come after Thompson, 50, was shot on a busy Manhattan street early on December 4 as he approached the New York Hilton Midtown on West 54th Street to attend his company’s annual investor conference while the killer waited for him, according to New York Police Commissioner Jessica Tisch.

The shooter then crossed the street from the Hilton and fled northbound through an alley between 54th Street and 55th Street. He rode off on an electric bike on 55th, investigators told CNN. From there, the suspect headed north on Sixth Avenue toward Central Park.

Police say the man was spotted near the George Washington Bridge and George Washington Port Authority bus terminal at 178th Street around 45 minutes after the shooting.

The killing of UnitedHealthcare’s CEO has rattled other health care companies concerned about their own leadership’s safety and prompted some of them to ramp up security and scrub top executives’ photos from their websites.

The backpack, photos, surveillance videos, ammunition left behind, a burner phone, a water bottle and DNA evidence have thus far helped investigators get closer to zeroing in on the suspect despite hitting dead ends with the use of facial recognition software and an unusable fingerprint previously obtained by police, according to Joseph Kenny, the NYPD’s chief detective.

Investigators continue to search for the electric bike the suspect rode the day of the shooting and are examining whether the shooter used a veterinary gun, a larger firearm used on farms and ranches to put down animals without causing a loud noise, Kenny said Friday.

Looking for a motive

The 9 mm shell casings undergoing testing had the words “delay,” “deny” and “depose” written across them, with one word on each of the three bullets, Kenny told reporters.

Police are looking into whether the words, similar in phrasing to a common description of insurance company tactics – “Delay, deny, defend” – may point to a motive.

“That might be him sending a message saying why it was that he shot (Thompson), but at the same time, it could be a diversion to try to get taken away from the real reason behind it,” former FBI Special Agent Kenneth Gray told CNN on Saturday.

“Until he’s caught, we won’t actually know the purpose of those words,” Gray said.

Authorities are seeking the public’s help identifying Thompson’s killer through surveillance images showing the unmasked suspect in an Upper West Side hostel where he checked in using a fake New Jersey driver’s license.

But with some portraying the killer as a vigilante enacting justice against a health care system they believe values profits over lives, and with other users on social media mocking the CEO’s death, it could hinder motivation to report sightings of the killer to police.

What’s next in the investigation?

Police are tracking down as many tips as they can, as the manhunt spreads and authorities try to determine where the suspect might surface.

NYPD officials said they believe the suspect left New York City on an interstate bus, the same mode of transportation investigators believe he used to get to the city days earlier: He traveled to New York on a Greyhound bus starting its route in Atlanta, multiple law enforcement sources told CNN. Those sources added authorities do not know whether the suspect boarded in Atlanta or elsewhere.

The Atlanta Police Department announced Friday, without elaborating, it will assist the investigation after the NYPD contacted it. NYPD detectives arrived in Atlanta on Saturday as part of the probe, two law enforcement officials briefed on the matter told CNN.

In the meantime, the gun remains the key piece of outstanding evidence police are searching for, building a case against the shooter for when he’s found.