New details are emerging in the case of UnitedHealthcare CEO Brian Thompson’s death, as a manhunt for the person of interest involved in the fatal shooting is on its third day.

Authorities do not yet have a name for the suspect at this time, according to NYPD Chief of Detectives Joseph Kenny.

But smiling photos showing a man police consider a suspect may have provided a significant clue as he lowered his mask during a flirtatious moment with a New York hostel clerk, CNN’s chief law enforcement analyst reported Thursday. Investigators have also found a backpack in Central Park that they believe belonged to the suspect.

Here’s what we know so far:

Ongoing manhunt:

Investigators have a “reason to believe” the person of interest in Thompson’s killing has left New York City, according to police commissioner Jessica Tisch.

The suspected gunman traveled by Greyhound bus to New York before the shooting, a source said. Authorities also said the suspect used a fake New Jersey driver’s license to check into an Upper West Side hostel. The hostel has since posted a notice to other guests, stating that it is cooperating with police in the investigation.

The Atlanta Police Department confirmed Friday that it is working with the NYPD as part of the investigation. The FBI is also assisting New York law enforcement, a bureau spokesperson told CNN on Friday.

The “money shot”

Officials had to sift through a substantial amount of video surveillance footage to obtain the images of the suspected gunman — pictures Tisch called the “money shot” during a Friday interview with CNN’s Shimon Prokupecz. She said police released the photos because they want a “wider audience to see the picture outside of New York City.”

This image has been sent to every member of the NYPD, a law enforcement official told CNN.

DNA evidence:

Detectives have recovered possible DNA evidence from items found at the scene and have now turned it over to a lab for testing, according to a senior law enforcement official briefed on the investigation. The swab samples are from a water bottle, which police believe the killer purchased and may have sipped from shortly before killing Thompson.

The various pieces of evidence being uncovered are crucial not only for finding the gunman — but also for his prosecution. Once police apprehend the person of interest they are looking for, the key is to be able to link him to the evidence, retired NYPD Detective Michael Alcazar told CNN on Friday

A message to UnitedHealth Group employees:

Andrew Witty, the CEO of UnitedHealth Group, the parent company of UnitedHealthcare, addressed employees in an internal video message Thursday, advising them to take care of themselves and letting them know that there are resources available to them in wake of Thompson’s death.

Witty acknowledged that employees are “nervous around security and safety” and detailed heightened security measures the company is implementing at its facilities nationwide, including security checks before people enter campuses.

Investigators are treating a backpack found in New York City’s Central Park like a dead body, being very careful not to damage any potential evidence, a law enforcement official told CNN.

The backpack was removed by an excavator along with any physical material found surrounding it, the source said. No officers picked it up to preserve potential DNA evidence tied to the backpack or even the dirt on the ground surrounding it.

Forensic investigators at a police lab in Queens will go through the contents of the bag slowly and deliberately and should have everything out of it by tomorrow. They will examine not only the contents of the bag but the bag itself, which may have sweat or other evidence of the shooter, the source said.

While this is happening, investigators are still searching for the suspect’s name. They believe he traveled to the city by bus and are in the process of ruling out a tip that the shooter left by plane.

Police have different leads and are currently going through them all. In addition to video canvassing, they are requesting bus manifests to see if there could be any identifying clues.

They have also reached out to the security team of UnitedHealthcare to get their complied person of interest list, looking for people that have been publicly vocal with complaints against the company, according to the source. They are asking about anyone who has used any vitriolic language and made threats, either on social media or through attendance at public demonstrations.

Most people on the list have already been dismissed through social media searches, the law enforcement source said. The rest are being looked into for any possible ties.

All the work being done is indicative of the massive undertaking this process is, the source said. The mandate is to continue to build a video timeline of every day the suspect was in the city. There is still no common area where he has gone multiple times.

Identifying the suspect is critical and multiple law enforcement agencies are offering to help in the search once an ID is made, the source added.

Police are using video surveillance to piece together the alleged gunman’s movements before, during and after the fatal shooting of UnitedHealthcare CEO Brian Thompson on Wednesday.

Some key moments:

6:15 a.m. ET: A surveillance camera image appears to show the suspect in the UnitedHealthcare CEO’s murder leaving the 57th Street F train station before the shooting. The image was recorded at 6:15 a.m. Investigators believe that the suspect may have taken a subway from the Upper West Side to midtown.

6:17 a.m. ET: Video at a nearby Starbucks shows the assailant buying a bottle of water and two energy bars roughly 30 minutes before the shooting, according to police.

6:19 a.m. ET: Surveillance video captured near a deli on W 55th street appears to show the suspect walking and briefly stopping by a pile of trash.

Around 6:30 a.m. ET: Surveillance video captured what appears to be the gunman on the phone.

6:44 a.m. ET: Thompson walked toward the Hilton Midtown after leaving his hotel across the street, police said. The masked gunman was “lying in wait” outside the Hilton as Thompson made his way to the hotel to attend his company’s annual investor conference, according to New York City Police Commissioner Jessica Tisch. The gunman came up behind Thompson and shot him in the back, NYPD Chief of Detectives Joe Kenny said. He then walked toward Thompson and continued to shoot, stopping to clear a gun jam before firing again, Kenny said.

View the full visual timeline of the shooting.