A man in the Altoona, Pennsylvania, area is being questioned Monday in connection with last week's UnitedHealthcare CEO killing in Manhattan, in part because he was found with a gun similar to the one used in the shooting, two sources familiar with the matter told NBC News.

The sources say it is too soon to determine if his case is connected to the death of Brian Thompson, but they are investigating it as a potentially significant development. According to the sources, customers at a local McDonald's thought he looked suspicious and called police. Arriving officers noticed a fake ID so took him in for questioning.

Once at the police station, the sources said, officers discovered the man had a gun similar to the one used in Thompson's killing, as well as a silencer and a fake New Jersey ID. The suspected gunman allegedly used a fake New Jersey ID when he checked into a Manhattan hostel last month.

Two senior law enforcement officials say the man in Altoona being questioned had the name "Marc Rosario" on his fake NJ ID. Three sources familiar with the matter say the suspected gunman checked into the hostel using a fake NJ ID with the name “Marc Rosario.”

The suspected gunman also may have taken a bus to get out of New York. Investigators are looking into whether the man being questioned had recently gotten off a bus from Philadelphia, according to a senior official. NYPD detectives are headed to the area to question the man, who sources said looked similar to the suspected gunman.

The development comes as a private funeral is being held Monday for Thompson, the 50-year-old executive gunned down at point-blank range as he headed to a midtown hotel for an investors' conference last Wednesday, according to a source familiar with the plans.

Five days after the shooting -- by a man captured on surveillance cameras across Manhattan -- the killer remains on the loose. The nation's largest police department is after him, along with the FBI. Despite obtaining a clear image of his face among other evidence, authorities have yet to identify him.

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Late Saturday, police released two additional photos of the suspected shooter that appeared to be 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 back seat and the front of the cab. In both, his face is partially obscured by a blue, medical-style mask.

The new photos came after authorities recovered a gray bag possibly belonging to the suspect in Central Park. The bag was taken, unopened, for forensic processing before investigators were to review its contents. Sources later said the bag contained a jacket and Monopoly money, but no gun. DNA testing is ongoing.

Retracing the gunman’s steps using surveillance video, police say, it appears he left the city by bus soon after the shooting Wednesday morning outside the New York Hilton Midtown. He was seen on video at an uptown bus station about 45 minutes later, NYPD Chief of Detectives Joseph Kenny said.

With the high-profile search expanding across state lines, the FBI announced late Friday that it was offering a $50,000 reward for information leading to an arrest and conviction, adding to a reward of up to $10,000 that the NYPD has offered. Police say they believe the suspect acted alone.

Hundreds of detectives are combing through video recordings and social media, vetting tips from the public and interviewing people who might have information, including Thompson’s family and coworkers and the shooter’s randomly assigned roommates at the Manhattan hostel where he stayed.

Tracking a killer

Aided by surveillance cameras on nearly every building and block, police have been able to retrace the shooter’s movements.

They know he ambushed Thompson at 6:44 a.m. as the executive arrived at the Hilton for his company’s annual investor conference, using a 9 mm pistol that resembled the guns farmers use to put down animals without causing a loud noise. They know ammunition found near Thompson’s body bore the words “delay,” “deny” and “depose,” mimicking a phrase used by insurance industry critics.

Kenny said 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 that he could possibly be a disgruntled employee or client.

Investigators know from surveillance video that the shooter fled into Central Park on a bicycle and ditched it around 7 a.m. near 85th Street.

He then walked a couple blocks and got into a taxi, arriving at 7:30 a.m. at the George Washington Bridge Bus Station, which is near the northern tip of Manhattan and offers commuter service to New Jersey and Greyhound routes to Philadelphia, Boston and Washington.

Investigators don't know what happened next. They are searching through more surveillance video but have yet to locate video of the shooter getting on a bus or exiting the station.

Police have determined from video that the gunman was in the city for 10 days before the shooting. He arrived at Manhattan’s main bus terminal on a Greyhound bus that originated in Atlanta, though it's not clear whether he embarked there or at one of about a half-dozen stops along the route.

Immediately after that, he took a cab to the vicinity of the Hilton and was there for about a half hour, Kenny said.

At around 11 p.m. on the night he arrived, he went by taxi to the HI New York City Hostel. It was there, while speaking with an employee in the lobby, that he briefly pulled down the mask and smiled, giving investigators the brief glimpse they are now relying on to identify and capture a killer.