NEW YORK – The police do not know who he is, where he is or why he did this.

Like UnitedHealthcare’s Frustrating Search CEO Brian Thompson As the killer was on his way for a fifth day Sunday, investigators were faced with a tantalizing contradiction: They have plenty of evidence, but the shooter remains an enigma.

However, they are convinced of one conclusion: it was a targeted attacknot a coincidence.

They know he ambushed Thompson at 6:44 a.m. Wednesday as the executive arrived at the Hilton for his company’s annual investor conference, using a 9mm pistol that resembled the weapons farmers use to fell animals without causing noise. They know ammunition was found near Thompson’s body carried the words “delay”, “refuse” and “deposit”, imitating an expression used by insurance industry reviews.

The fact that the shooter knew UnitedHealthcare Group was holding a conference at the hotel and what route Thompson might take to get there suggested it could possibly have been a disgruntled employee or customer, said New York Police Chief of Detectives Joseph Kenny.

Over the weekend, police divers were seen searching a pond in Central Park, where the killer fled after the shooting. Officers have been scouring the park for days looking for possible clues and found his backpack there on Friday. They did not immediately reveal what, if anything, it contained, but said it would be tested and analyzed.

As of Sunday afternoon, police declined to comment on the contents of the backpack or the results of the pond search, saying no updates were planned.

The bag’s apparent manufacturer did not immediately respond to questions from The Associated Press.

Investigators urged patience, saying the process of recording evidence presented in court is not as quick as it would have been. it looks like it’s on TV.

Hundreds of detectives are scouring video recordings and social media, checking tips from the public and interviewing people who may have information, including Thompson’s family and co-workers, as well as roommates randomly assigned to the hostel shooter from Manhattan where he was staying.

Investigators got pause when they came across security camera footage of an unsupervised moment at the inn in which he briefly showed his face.

Tracing the shooter’s steps using surveillance video, police said, it appeared he left the city by bus shortly after the shooting outside New York’s Hilton Midtown. He was seen on video at a downtown bus station about 45 minutes later, Kenny said.

As the high-profile search stretches across state lines, the FBI announced Friday evening that it will offer a $50,000 reward for information leading to an arrest and conviction, adding to the reward of up to $10,000 offered by the New York Police Department. Police say they believe the suspect acted alone.

Police have distributed the images to the media and on social media, but so far have been unable to identify him through facial recognition – perhaps due to the angle of the images or limits on how the New York Police Department is allowed to use the technology, Kenny said.

On Saturday evening, police released two additional photos of the suspected shooter, which appeared to come from a camera mounted inside a taxi. The first shows him outside the vehicle and the second shows him looking through the partition between the rear seat and the front of the cabin. In both cases, his face is partially obscured by a blue medical-style mask.