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TAMPA, Fla. — Romano Whitley had just gotten home on Oct. 11 when she heard it: pop-pop-pop-pop-pop.

Whitley believed the sounds were firecrackers, and after peeking out the bedroom window of her home in Seminole Heights, a residential section of Tampa, she thought little more of it.

"I didn't see a car," Whitley said. "I didn't hear anybody scream."

In fact, the pops were gunshots striking Monica Hoffa, 32, a sign language teacher, whose body was discovered two days later, after Whitley asked that the overgrown grass in a nearby city-owned lot be mowed.

"No one could see her in the grass," she said, adding: "We feel horrible."

Hoffa is one of three victims in a series of killings that authorities now believe are linked: The first apparent victim, Benjamin Mitchell, 22, a community college student, was shot dead while waiting for a bus on Oct. 9. Anthony Naiboa, 20, was killed last Thursday after taking the wrong bus home from work. His body was found 300 yards from Mitchell's.

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Police have not yet identified a suspect or determined a motive. The killings were committed within a 1-mile radius over two weeks, sending a ripple of anxiety through this historic neighborhood of breweries and restaurants, bungalows and Victorians.

"There's no rhyme or reason, so we all feel a little shaken and concerned that we could be the next victim," said Stan Lasater, president of the Southeast Seminole Heights Civic Association.

"We've always had small, petty crimes," Lasater said. "But when we had the first murder, the community was really shaken. And then we had the second, and third, and now the community is definitely on alert."

Tampa Police Chief Brian Dugan said the deaths were "terrorizing" the neighborhood, but he urged residents to carry on as usual — to have barbecues, to walk their dogs, to turn their porch lights on.

"We're not going to be held hostage," he said.

Dugan has declined to describe the string of deaths as the work of a serial killer, saying too little is known about the crimes.

"I have purposely avoided that labeling because I don't want people to focus in on one person," he said. "We don't know if it's more than one person [or] a team of people."

A picture of Anthony Naiboa, 19, is held during a vigil for three people were found murdered in less than two weeks in Seminole Heights near Tampa, Florida. WFLA-TV

In the meantime, residents veer between vigilance and anxiety. Whitley said she's been up all night, staring out the window, while Lasater said the association is helping promote a porch light campaign — "We're making it harder for this guy to sneak about the neighborhood unseen," he said — and coordinating with police to make sure people get accurate information.

In a show of defiance that doubled as a kind of memorial, people marched through the neighborhood on Friday, placing flowers and candles at the three locations where people were killed. A vigil was also held Sunday, NBC affiliate WFLA reported.

The victims' relatives, meanwhile, were struggling to make sense of their losses and what they had done to the neighborhood.

"Everybody's locking their doors, and you shouldn't have to live like that," said Angelique DuPre, Mitchell's cousin. "You shouldn't have to be afraid to stand outside at 7 o'clock at night because some crazy person just takes it upon themselves ... to take this person's life."

DuPre said Mitchell, who worked at Ikea to pay for classes at Hillsborough Community College, where he studied business, was catching the bus to see his girlfriend the night he was killed.

He pleaded with his cousin's killer to surrender.

"You're hurting families that [are] going to live with this for the rest of their lives," he said. "Before you feel like you need to take somebody else's life, turn yourself in."

Maya Rodriguez reported from Tampa. Tim Stelloh reported from Alameda, California.