The suspected gunman sought in the killing left New York City after the murder on a bus headed toward Atlanta, Fox News has learned.

The suspect arrived in New York last month on a bus from Atlanta, authorities previously said.

NYPD investigators were working local, state and federal law enforcement on the case.

The search for the suspect is nationwide, police said.

Fox News' Alexis McAdams contributed to this post.

​

Investigators in the fatal shooting of UnitedHealthcare CEO Brian Thompson are engaging in a "deep dive" into his personal life, including his family and friends, a retired NYPD officer told Fox News Digital Friday.

"In this case, I think what the cops are really looking at, what the investigators are really looking at is the victim because the overwhelming majority of homicides are committed by someone the victim knows," Ralph Cilento, a retired lieutenant commander of detectives at the NYPD and adjunct professor of police science at John Jay College of Criminal Justice, explained.

"It's a very high percentage, like near 90%, I think. So, other than the crime scene analysis, what goes on forensically, what recovered shell casings and live rounds and things like that [there are] in every homicide – not just this one – there is a deep dive into the victim."

He said even if the victim didn’t know the suspect, they may have known each other "by proxy if someone sent an assailant to kill somebody."

"So, generally, the way you investigate homicides, among other ways, is you start with the victim and you make concentric circles out, and usually the perpetrator is in there somewhere. Not always, but usually," he explained.

Cilento also noted that the shooting happened the morning of the Rockefeller Center Christmas tree lighting.

Fox News Digital's Brie Stimson contributed to this post.

​

Paul Mauro, a retired NYPD inspector, retraced the steps taken by the gunman before and after the killing of UnitedHealthcare CEO Brian Thompson on a New York City street earlier this week.

“The shooter knew where to go, before and after,” Mauro said, meaning he planned the deadly attack and possibly walked the route he took on the morning of the murder and did some “reconnaissance.”

The alleged first gunman was seen at a Starbucks in Midtown Manhattan and walked toward where the shooting occurred. He didn't have the bicycle he was spotted with after the shooting, Mauro said.

“Some place in here, there's a bicycle waiting for him that he acquires after the event,” Mauro said.

Once in an alley where he presumably walked near where the shooting took place on West 54th Street, he still didn't have a bicycle, which could have been stashed somewhere nearby, Mauro said.

Just before he opened fire, the shooter waits for Thompson close by before shooting, during which the weapon appeared to jam. Three spent casings with infamous messages were found at the scene , as well as three live rounds.

After the shooting, the gunman comes back through the alley he came.

“Some place back there, the bike was stashed,” said Mauro. “How and by whom, we don't know."

Once out of the alleyway, the shooter dropped his burner phone.

“He almost certainly walked this route and did some reconnaissance before he did the shooting,” said Mauro.

He added that investigators will most likely review camera footage from the area before in the days before the shooting to see if he canvassed the area. The masked shooter arrived in the city several days before the killing.

After the killing, the alleged shooter rode toward Central Park on a bicycle.

“That's kind of where he goes dark to the police and to cameras,” until he exits the park on the Upper West Side," Mauro said. “He was probably in that park within two or three minutes, and from there, and the size of that park, it's a needle in a haystack.”

Fox News Digital's Julia Bonavita contributed to this post.

​

A retired FBI special agent told Fox News Digital that tips are likely “pouring in” to the NYPD because of the full face shot released of the UnitedHealthcare CEO shooting suspect in the same way they did with the Boston Marathon bombing in 2013.

“In Boston, we had photos of 'black hat' and 'white hat' in the marathon bombings, but they weren’t really clear and they didn’t really add any investigative value because if you put those out they really didn’t look like anybody,” Jason Pack, a retired FBI special agent who investigated the bombing, told Fox News Digital on Friday, referring to the bombing suspects Tamerlan Tsarnaev and Dzhokhar “Jahar” Tsarnaev.

He said once investigators got a “clear photo” of the suspects “several hours later the tips started pouring in and I’m sure that’s going on right now with the NYPD with the clear face shot of the suspect.”

He added that tips from the public are “really important” and that the FBI has a saying “the greatest weapon we have against crime is cooperation and support of the American people.”

On Thursday, the NYPD released a photo of the suspect in the killing of UnitedHealthcare CEO Brian Thompson in which he was smiling in the lobby of a Manhattan hostel.

​

It's hard to believe that authorities haven't identified the gunman who killed UnitedHealthcare CEO Brian Thompson on a New York City street this week, a former FBI agent said.

Despite images and video footage of the unmasked suspect being widely circulated, investigators have not been able to identify him.

“It's absolutely shocking to me that we don't know who this person is right now, and not because of the lack of effort on the part of the New York Police Department, Ret. FBI special agent Maureen O'Connell told ”Your World Cavuto."

Investigators will most likely try to use forensic genecology using the suspect's DNA and genecology sites.

“They're going to see if they find any other people that match him closely. With any luck, his mom or his brother did Ancestry (.com) and we'll be able to find out who this person is rather quickly," O'Connell said.

Investigators in New York City believe they have found the backpack used by the gunman sought in the killing of UnitedHealthcare CEO Brian Thompson during a Friday search of Central Park.

Investigators say the gunman went into Central Park after the shooting with his backpack on and a short time later came out without it. The bag was found not far from the popular park carousel.

Authorities were sweeping the park to find the bag, searching through lakes and ponds, meadows, playgrounds and a densely wooded section called “The Ramble.”

As dusk approached Friday, small groups of officers could be seen roaming among trees across ground covered with leaves.

Video of the gunman fleeing Wednesday’s shooting showed him riding a bicycle into Central Park and later taking a taxi to a bus terminal that offers commuter service to New Jersey and Greyhound routes to Philadelphia, Boston and Washington, D.C, Chief of Detectives Joseph Kenny told reporters earlier.

Fox News' Alexis McAdams and The Associated Press contributed to this post.

​

The New York Police Department on Friday said investigators believe the assailant left the city after killing Thompson in Midtown Manhattan on Wednesday.

Retired NYPD detective Pat Brosnan told Fox News that the killer authorities will track the gunman down no matter where he is. His biggest mistake was flirting and smiling with a receptionist at the hostel where he stayed for several days.

“That put his picture out there to the globe and it's viral. There's no place he can hide. I'm not even remotely concerned with the statements from the commissioner as it related to him leaving the five boroughs of New York,” he said.

“I'm taking the over-under here. He's in leg irons within days, if not hours,” he added.

Brosnan also noted that New York City has thousands of cameras, some of which captured images the suspect before the killing.

“If this guy thinks that he's going to remain invisible under that unblinking eye and army of cameras, he's sadly mistaken,” he said.

Health insurer Medica has temporarily closed its Minnesota headquarters as the manhunt for the gunman who killed UnitedHealthcare CEO Brian Thompson continues.

A Medica spokesperson told FOX 9 safety concerns prompted the health plan company to close its offices temporarily through at least Dec. 13

"The safety of Medica employees is our top priority and we have increased security both for all of our employees. Although we have received no specific threats related to our campuses, our office buildings will be temporarily closed out of an abundance of caution. Like other insurers, Medica also has removed from our website the bios of its executives, for the same precautionary reasons."

Authorities have not determined a motive for Thompson's killings but health insurance companies have taken steps to reduce the visibility for its executives, the news station reported.

In a statement on LinkedIn earlier this week, Medica called Thompson “a visionary leader in the healthcare space.”

An unidentified gunman approached UnitedHealthcare CEO Brian Thompson from behind Wednesday morning and opened fire outside the New York Hilton Midtown in Manhattan, then vanished into the streets of the Big Apple, prompting a large-scale manhunt.

Authorities have not revealed a motive, but after bullet casings at the scene were found with words "deny", "depose" and "defend" written on them – a possible reference to the book "Delay, Deny, Defend: Why Insurance Companies Don't Pay Claims and What You Can Do About It" – speculation swirled that the slaying may have grown out of resentment for a denied claim.

Thompson was separated from his wife, Paulette, at the time of his death and the Minnesota-based firm's parent company laid off workers in multiple states in September, according to The Star-Tribune.

Wednesday, Dec. 4

Around 6:14 a.m.: Before the attack, the NYPD recovered a surveillance video from a Midtown coffee shop showing the masked suspect, and surveillance video from outside the Stage Star Deli near the corner of 55th Street and Sixth Avenue shows him passing by multiple times minutes later.

By 8 a.m., the gunman is believed to have entered the Port Authority Bus Terminal and taken a train out of the state.

Police traced his route from the crime scene near 54th Street and Sixth Avenue up to Central Park, which he exited at 77th Street and Central Park West, Chief of Detectives Joseph Kenny told Fox News Friday.

Read more about the timeline on the killing of UnitedHealthcare CEO Brian Thompson.

​

The speculation regarding the shooting of UnitedHealthcare CEO Brian Thompson continues to run rampant. While this can be interesting, the truth is that the on-the-ground investigation will be far more prosaic than glamorous. For today’s detectives, serious crime investigation marries grinding "shoe leather" work to data-driven digital forensics. It can be a daunting amount of information.

1. ‘Hitmen for hire,’ in the commonly perceived sense, don’t really exist

The idea that someone off the street can walk into a social club or call-a-guy-who-knows-a-guy who kills for a living is essentially a myth – I cannot recall one in my experience. That said, murders-for-hire do exist (i.e, an associate who is not a "professional" is willing to hire on).

2. The timeline is key

Currently – and this is unsurprising – the tip line regarding the case is blowing up. But what detectives are most focused on are the indicators they can depend on, like: How did the shooter know that Thompson would show up for an 8:00 a.m. conference at 6:40 a.m.? Did the shooter have some access to Thompson’s schedule or movements?

3. How did the shooter so instantly recognize Thompson?

The shooter was along the building line across the street when Thompson came up the block. Video shows the shooter apparently recognizing Thompson from what must be at least 60 feet, in twilight, early-morning conditions. Again: How did he know Thompson was coming?

Read more about the six key data points in the NYPD investigation into the killing of Brian Thompson by Fox News contributor Paul Mauro.

​

UnitedHealth Group said Thursday it is grieving the loss of CEO Brian Thompson after a lone gunman shot him in broad daylight outside of the Hilton in Midtown Manhattan earlier this week.

The company said Thompson was "a highly respected colleague and friend to all who worked with him".

On Thursday the healthcare company issued its second statement since the incident occurred to express their gratitude for the kind words and sympathy of Americans across the country.

"While our hearts are broken, we have been touched by the huge outpouring of kindness and support in the hours since this horrific crime took place," the statement read.

"So many patients, consumers, health care professionals, associations, government officials and other caring people have taken time out of their day to reach out. We are thankful, even as we grieve," they went on to say.

The New York Police Department has been hunting for the killer since early Wednesday morning.

Read more about the killing of UnitedHealth Group CEO Brian Thompson.

The New York City Medical Examiner's Office confirms that it is examining DNA evidence connected to the assassination of UnitedHealthcare CEO Brian Thompson early Wednesday.

"We can confirm that OCME’s (Office of the City Medical Examiner) DNA laboratory is analyzing evidence submitted by law enforcement," a spokesperson told Fox News Friday. "That is the extent of details we can provide."

The ME's office is typically limited in what it can sure during an investigation, confirming whether it is involved in one and the cause and manner of death.

A masked gunman shot Thompson from behind outside a Manhattan Hilton hotel around 6:45 a.m. Wednesday as he was on his way to the venue for a company conference. Surveillance video shows the assailant sneaking up from behind and opening fire before walking away from the crime scene.