CNN
—

Police are questioning a man in Altoona, Pennsylvania, in connection with the fatal shooting nearly a week ago of a top U.S. health care executive on a busy New York City street, two law enforcement officials familiar with the matter tell CNN.

Acting on a tip-off, police stopped a person traveling on the bus and confiscated a silencer – a device that muffles the sound of a firearm – and a number of false IDs, an official added.

The man is now in custody and is being questioned.

The development comes amid an intensive search for whoever fatally shot UnitedHealthcare CEO Brian Thompson.

Authorities know what the suspect looks like, but don’t know who or where he is. From the fleeting glimpse of his unmasked face, his movements through the country’s largest city, and the possessions he allegedly threw away, the police seem almost familiar, but remain a mystery.

The public has also seen the suspect in surveillance photos and videos – including one in which he pointed the gun at Thompson’s back – as he continues to evade capture in the Dec. 4 killing outside a midtown Manhattan hotel.

The suspect was believed to have left New York City on an interstate bus, law enforcement officials said, after video cameras caught him entering but not leaving the George Washington Bridge bus station at 178th Street.

Here are other key developments:

Given the suspect’s past missteps – and the mistakes he could make during the manhunt – establishing his identity will likely help identify patterns that lead to his eventual arrest, experts told CNN. With tips mounting and probably hundreds of authorities looking for him, how long can he avoid getting caught?

A determination of the suspect’s identity is likely to come soon, said former FBI profiler Mary Ellen O’Toole.

“I think we’ll know who that is in a few days, if anyone,” she told CNN. “He is completely outnumbered. With this kind of manpower behind them, they will find the information that will identify him.”

Experts say the suspect made missteps before and after the attack that could bring authorities closer to finding him.

“The ability to fight back against an investigation like this is not something one person can achieve, no matter how arrogant you are,” O’Toole said. “You’re bound to make mistakes.”

Some of the suspect’s actions — such as pulling down his mask on camera and leaving behind labeled bullet casings that could indicate a motive, a flashlight phone and a partial fingerprint on a water bottle — have only strengthened the clues left behind for authorities .

Police also tracked his movements on a Greyhound bus traveling from Atlanta to New York City before the shooting.

“What hurts the shooter is that law enforcement is getting better, but the shooter can’t undo what he’s already done,” O’Toole said.

The gunman appeared to have perhaps only practiced such killings before and was not an experienced assassin, O’Toole said. Leaving bullet casings or Monopoly money to authorities would not normally be consistent with the actions of a murderer who wanted to “get back into oblivion,” she said.

Police are continuing to investigate whether the words found on the casings — “delay, deny, defend,” said NYPD Chief Detective Joseph Kenny — could indicate a motive. A 2010 book criticizing the insurance industry is titled “Delay Deny Defend,” a common description of its tactics.

Minimizing the number of actions a fugitive takes before and after a crime is crucial to avoiding getting caught, said Peter Young, a former FBI fugitive who spent more than seven years avoiding arrest on terrorism-related charges the release of animals from fur farms.

“It sounds like this person didn’t comply,” Young told CNN. “If he were to stop at Starbucks, that sounds like an unnecessary risk.”

Under pressure and no more options

After evading capture by the FBI, New York Police Department and other agencies for several days, the psychological pressure of escape and the focus of a large-scale search could lead to mistakes, O’Toole said.

“It would be absolutely overwhelming and there’s nothing he can do about it and this is where he’s going to make mistakes,” she said. “In the role of the shooter, he is currently having to deal with emotions and consequences that I don’t think he expected at all.”

It’s possible that under increasing pressure, the suspect could lose the critical thinking skills he needs to strategically avoid capture, the expert said.

“His options are becoming fewer and fewer, and beyond that his ability to make good decisions is deteriorating,” O’Toole said.

“(Given the fact) that he will never be able to return to a normal life like he had before last week, all of this can lead to very bad decisions,” she added.

As investigators focus on the suspect and his identity, they can examine details about his life that could be crucial to the case, O’Toole said.

“They will be looking for his behavior patterns,” she said. “You start asking, ‘Where does he work?’ Where does he go after work? Does he work out in the gym? Does he walk his family dog?’

“It is really difficult for us to break any pattern of behavior that we rely on in our lives. So at some point you default to going to Starbucks to get your coffee, or you default to getting up at 6 a.m. and going for a run,” she added.

The morning before the shooting, the suspect was seen ordering a bottle of water and two energy bars from Starbucks, images released by authorities show.

New photos released early Sunday by the FBI and NYPD show the hooded suspect wearing dark clothing sitting in the back of a taxi. His face is partially covered by a blue mask, while his eyes appear to be staring directly into the taxi’s camera.

Similar photos show him outside the taxi and appearing to be walking down the street.