-- Next to the balloons and flowers dressing a makeshift memorial in Tampa, Florida, Casimar Naiboa helplessly clutched a portrait of his slain son wearing his cap and gown.
In the year-old photo, Anthony Naiboa, the eldest of five siblings, was shown graduating Tampa's George S. Middleton High School.
"This was the proudest moment of my life," the father told ABC News.
Last Thursday, his 20-year-old son became the third targeted victim of what Tampa Bay Police believe are killings being committed by the same person or people.
The night Naiboa was slain, he had just finished his work shift and was waiting for the No. 9 bus, his father said. After it failed to come, he started walking on 15th Street near Wilder Avenue to catch an alternative bus home.
"He was waiting for the bus a while and decided to walk a little bit," Casimar Naiboa said.
Then, Naiboa was shot. By the time responders reached him, he could not be resuscitated.
"It was too late," Dugan said. "He was already dead when our police officers came upon him."
Since Naiboa was fatally gunned down, Tampa Police Chief Brian Dugan told ABC News that he has advised cops to be extremely vigilant.
"When I spoke to the guys at the briefing, I told them that, 'Everybody out there is a potential suspect or a potential victim and [you] need to think like that,'" he said, standing next to the victim's family.
"We have someone terrorizing the neighborhood," he said, vowing that his fellow cops, FBI and Bureau of Alcohol, Tobacco and Firearms (ATF) agents are committed to arresting the killer or killers.
"We're in this for the long haul, and we're going to find this person," Dugan said. "When I think about the victim and their families that's what gets us out of bed."
Tampa Mayor Bob Buckhorn echoed Dugan in a series of tweets Monday evening, saying that over 1,000 streetlights have been added to the Seminole Heights neighborhood. "We can't replace the lives that were taken or replace the holes in some of these families but we can ensure that whoever did this pays," he wrote. "... We're not stopping until we catch this guy."
The police chief said residents should not live in fear, but suggested that they put their porch lights on, go out in groups and "do cookouts."
"We're not going to be held hostage by whoever's doing this," he said.
So far, pixelated images of a person of interest have been circulating.
The police chief said that the killer or killers have managed to elude police.
"Whoever is doing it is able to vanish very quickly," Dugan said.
Naiboa's murder happened only 200 to 300 yards from where 22-year-old Benjamin Mitchell, who also attended George S. Middleton High School, was shot and killed on Oct. 9.
The young man, who was waiting at a bus stop located at North 15th Street at Frierson Avenue, died steps away from his home, Dugan confirmed.
On Oct. 13, Monica Hoffa was found slain a half-mile from Mitchell and Naiboa, Dugan confirmed.
The 32-year-old woman's remains were discovered in a vacant lot at New Orleans Avenue East, he said. She died two days prior.
A neighbor who lived on the block for 19 years heard the shots that led to Monica's untimely death.
"I was working on a paper for school," the 30-year-old master's student, who requested not to be named, told ABC News. "I heard five pops. It was in rapid succession."
He said cops questioned him after Hoffa's body was found.
The man told them at the time of the attack, he wasn't sure if the "pops" were firecrackers or actual bullets, so he kept working and didn't call 911.
A reward of $25,000 is being offered by Crime Stoppers to anyone who can help authorities "find person/s who murdered these Seminole Heights victims," according to a tweet posted by ATF
Chief Dugan described Mitchell as a "good person who comes from a good family" and said that while Hoffa "had some challenges in her life," there is no reason to believe there was motive to kill her.
Her uncle came to the memorial mourn her loss, but said the person who stole away his niece is still a threat.
"He's still out there," Robert Hoffa told ABC News. "Unfortunately the bad thing about it, we're still wondering who and why and where he is."
The loss is especially hard because there were no warning signs.
"She loved everybody," Robert Hoffa told ABC News. "She didn't have any enemies."
Hoffa, he said, "had only joy in her heart" and left a positive impression on others who came in contact with her.
"It's terrifying all this happening," he said, and noted that his brother, Hoffa's father, was broken by the loss.
"He's not good."
With a killer allegedly preying on loners, possibly still in town and on the loose, the manhunt has intensified.
Police continue to consider the similarities between the victims' situations.
Each of the three victims was alone and each was fatally shot while near bus stops.
Adrian Acier has lived in the Seminole Heights neighborhood for two years and told ABC News he heard shots from one of the three murders while he was watching television.
"The first one was really fast and then there three of them later," he said. "Minutes later a policeman came to my door."
The neighbor said more cops returned at around 2 a.m. the same night and he allowed them to search his home.
"I see police cars and undercover police driving around all the time," he said. "Everybody's worried and everybody has that scar that something's wrong."
The beefed-up police presence will continue, Dugan said, adding that the area has been "blanketed" with officers.
Police are not labeling the suspect as a serial killer at this point, but are not ruling anything out.
"I go from frustration to anger on these unsolved homicides," Dugan said. "We have someone who is terrorizing the neighborhood. It’s just difficult to see this happen."