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After a day of hunting for a suspect in the assassination, investigators pleaded for help from the public.

The gunman who fatally shot the right-wing activist Charlie Kirk remained on the run Thursday as a frantic and fruitless hunt for the killer led law enforcement officers to scour through chicken coops and plead for the public’s help.

With no suspect identified, investigators shared blurry photographs of a person of interest, which showed a man in a stairwell shortly before the shooting, wearing a hat and sunglasses. Officers also scrutinized a bolt-action rifle that they believe was used in the attack and sought to identify the gunman with other video from security cameras on campus.

“We are confident in our abilities to track that individual,” Beau Mason, the commissioner of Utah’s Department of Public Safety, said on Thursday.

But more than a day after the killer fired from a rooftop vantage point, jumped from the building and disappeared into a neighborhood nearby, investigators struggled to piece together a clear picture of who the gunman was and where their quarry had gone. The F.B.I. director, Kash Patel, and his deputy, Dan Bongino, were traveling to Utah to more directly oversee the manhunt.

Much of the early phase of the investigation had focused on a normally quiet residential street directly up a hill from Utah Valley University. Residents there said they had endured many hours of police searches and frantic law enforcement activity on Wednesday evening as heavily armed officers zeroed in on the area.

Local and federal officers, including agents from Homeland Security Investigations and the F.B.I., roamed the streets, knocking on doors and asking residents for footage from their doorbell cameras. As night fell, they combed a wooded area at the edge of some residents’ backyards with flashlights, an area where some in the neighborhood thought the officers recovered what was believed to be the shooter’s gun.

“It was kind of intense, very unsettling,” said Robin Harris, 41, who said police officers came to her door six separate times. At one point, she was startled by someone moving around her backyard, before realizing it was a police officer. Much of the early police activity centered around a house owned by the university that is under construction, with local residents seeing officers and dogs searching the property. Dylan Hope, 26, one of the construction workers at the house, said his crew was busy working on Wednesday afternoon when they heard a loud crack come from campus. Minutes later, Mr. Hope said, an excavator operator working on the site encountered a young man who said there had been a shooting. The interaction came almost immediately after the shooting, before any police officers arrived, Mr. Hope said. “He said somebody had been shot, and he was just trying to get home safe,” Mr. Hope said. “He seemed calm and stuff. He was shocked that someone had been shot.” About an hour after the shooting, Mr. Hope said that law enforcement officers arrived and showed the construction workers a photo of a man that they thought matched the description of the person the excavator operator had seen. Mr. Hope said the photo the officers showed the crew on Wednesday did not seem to look like the one the F.B.I. released to the public on Thursday.

Emergency radio traffic in the minutes after the shooting suggested a chaotic search for leads. There was talk among officers of various people who might be connected: a man dressed in a suit, a person who seemed to be going to hospitals looking for Mr. Kirk, someone who had removed an anti-Kirk post online, someone with a bionic arm.

At least two people were detained: A bespectacled man was dragged by police officers into a vehicle just minutes after Mr. Kirk was shot. Hours later, another man was taken into custody by investigators, a development celebrated by Mr. Patel on social media.

But in both instances, investigators found, the men had no connection to the shooting. The first one was a local political gadfly who was charged with obstruction of justice.

The other was a fan of Mr. Kirk’s who had attended the rally with friends. His name had been raised in emergency radio chatter and soon spread through social media. Family members said the man had gone home after the event, shaken and saddened by what had transpired, only to have investigators show up at his door to bring him in for questioning.

The man was able to show investigators video of the event that appeared to depict him standing in the crowd with his arms crossed as the gunshot rang out, the family members said. Investigators said they concluded that he was not involved. The fact that the shooting occurred at an outdoor event, attended by thousands of people, made nailing down and containing a perpetrator difficult from the beginning.

The event had been staffed by six police officers and Mr. Kirk’s own security team, according to the university police chief, Jeff Long. But investigators believe the gunman fired from the top of a building hundreds of feet away.

After the initial search through the neighborhood, investigators spent the overnight hours scouring through campus surveillance video, locating the images that they released on Thursday.

Investigators said they had also collected a footwear impression, a palm imprint and forearm imprints for analysis. They were reviewing some 200 tips.

The rifle that was recovered, a .30-06 Mauser, was located in a “wooded area where the shooter had fled,” Mr. Mason said. Investigators also recovered several cartridges, including a spent round in the rifle’s chambers, and sent them to be examined by analysts.

The search the previous day had proved unnerving for many residents.

Esther Whitney, 48, said she had been driving home from a Walmart when she learned there had been a shooting not far from her house.

“By the time I got home, there were already police, snipers across the street looking around for people, helicopters, lots of sirens and drones,” she said. At one point, Ms. Whitney realized the door of her chicken coop was hanging open.

“I actually went down with a baseball bat, cause I was like, ‘What if it’s the guy, and he’s hiding in there?’” she said. Then she realized it had been law enforcement officers searching through possible hiding places.

By Thursday afternoon, the activity had calmed significantly, but police cars were still watching the area, and yellow crime tape cordoned off a nearby stretch of street next to the campus. And homeland security officials were still knocking on doors.

Residents, meanwhile, were continuing to check in on each other. Ms. Whitney said she was making sure everyone was accounted for as part of her responsibilities as block captain.

“It’s kind of surreal that something this big happened in our backyard,” she said.