Foot traffic in Seminole Heights dried up, as fear – and additional police – saturated the neighbourhood. A week went by without incident. Then another week.

Halloween festivities, which seemed all but certain to be cancelled, proceeded cautiously, with Tampa’s mayor and interim police chief joining children to trick-or-treat as a show of faith in the community.

Even as police tried to determine whether they had a serial killer on their hands, daily life in Seminole Heights marched on. Early on Tuesday, however, any renewed sense of security was shattered when a fourth killing occurred, blocks from where the others took place.

Police responded to a shooting call and found Ronald Felton, 60, dead in the street.

“I know the big question’s going to be: Is this related to the other Seminole Heights murders?” interim Tampa Police Chief Brian Dugan said at a news conference. “And right now we are treating it as though it is related until we can rule otherwise.”

Felton had been crossing Nebraska Avenue, one of the neighbourhood’s main north-south thoroughfares, when a man came up behind him and shot him, Dugan said.

Previously homeless, Felton volunteered twice a week with a food bank at the intersection where he was found, Cynthia Murray, 68, told the Tampa Bay Times. Felton’s sister described him as “a quiet, peaceful person who would not bother anyone.”

“He was the type of person who would give you the shirt off his back,” Tina Felton told the newspaper. She had warned her brother in recent weeks to be careful because of the unsolved shootings.

Unlike in the three earlier killings, this time police had a description of the suspect, thanks to a witness who heard a gunshot and saw someone running away from the scene on foot. The suspect was described as a black male with a light complexion, about 6 feet tall, with a thin build; he was dressed in all-black clothing and had a large pistol, police said.

Dugan told reporters he thinks the suspect lives in the neighbourhood, and he urged residents to be vigilant.

“This has got to stop, and we will hunt this person down until we’ve found them,” Tampa Mayor Bob Buckhorn said on Tuesday.

Police had in late October released surveillance video of a figure running away from one of the earlier shooting scenes. Investigators have not yet identified the person of interest in that video, and the footage is “very much still relevant” to the investigation, Tampa police spokesman Eddy Durkin said.

Authorities said investigators have been working non-stop to track the killer – or, perhaps, killers – since the first victim was found dead on October 9.

Benjamin Mitchell, an aspiring musician and community college student, was shot while standing alone at a bus stop, police said.

Four days later, officers discovered the body of 32-year-old waitress Monica Hoffa in a vacant lot about 10 blocks from where Mitchell was found.

Then, on October 19, they found the body of Anthony Naiboa, 20. According to his father, Naiboa, who had a mild form of autism, had probably got aboard on a different bus after his usual route was shut down, and was unfamiliar with Seminole Heights.

He was walking home when he was killed, police said.

The common thread was the Route 9 bus, which meanders on a north-south path from the University of South Florida to downtown Tampa. The bus has since been re-routed, and officials have taken other measures to safeguard the community.

“It’s been a very rough couple of months,” Seminole Heights resident Renee Campbell told The Washington Post. “We’ve had to change all of our patterns, if you will. We don’t walk the dog any more twice a day. We don’t sit outside as much as we used to. We used to sit on the front porch and chat after dinner. Now we do it in the backyard, if we go out at all.”

Brent Stoehs, who has lived in the neighbourhood for 13 years, woke up to the sound of a police helicopter on Tuesday morning and thought, “Yep, another one.”

Since the homicides began, he has noticed increased police presence and less foot traffic after dark. On Tuesday, local and federal law enforcement officials set up a command centre at Seminole Heights Baptist Church, just northwest of the lockdown area. A van from the Bureau of Alcohol, Tobacco, Firearms and Explosives was surrounded by Tampa police cars of all shapes and sizes.

Many businesses were closed and a helicopter buzzed overhead.

“Everyone is on edge,” said Stoehs, 37. “This is crazy. We’ve never had anything like this.”

Rick Fifer, who lives and works in Seminole Heights and owns Vintage Homes Realty, has noticed far fewer pedestrians and had a couple of people cancel home showings because they got “cold feet” after the shootings.

Fifer said his dog’s incessant barking woke him up on Tuesday as police cars and helicopters converged on the neighbourhood.

The latest killing, he said, occurred less than a mile south of his home – and within a block of his office.

“I’ve lived in this neighbourhood for 25 years, and we’ve never had anything like this. It’s unnerving,” said Fifer, 55. “It does affect your thinking. If I go to put the trash out and it’s midnight, I start thinking and wondering and looking around more than I used to.”

Fifer said he stayed indoors on Halloween and has heard from neighbours who feel jumpy just passing someone on the street.

“People shouldn’t have to live that way,” he said.