Reward upped to $100K as Tampa police search for answers in 4 unsolved murders in 6 weeks

— -- The reward to help find a killer on the loose in Tampa, Florida, has increased to $100,000 as investigators search for answers.

A string of unsolved killings in the Seminole Heights neighborhood has left the community on edge. Four people have been shot and killed within blocks of one another in just six weeks.

The reward for information leading to an arrest stood at $91,000 until Tampa restaurateur Richard Gonzmart pledged $9,000 on Thursday. Law enforcement partners have contributed $85,000 and the community has raised more than $6,000, according to the Tampa Police Department.

"The support from the community and our law enforcement partners has been inspiring," Tampa Police Chief Brian Dugan said in a statement Thursday. "I can't thank them enough for stepping up. The reward money is truly impressive, and that's only one of the many ways that people are showing their support."

The first three victims were killed within 11 days in October. Benjamin Mitchell, 22, was killed on Oct. 9 and then the body of 32-year-old Monica Hoffa was found on Oct. 13, just half a mile from where Mitchell was killed. Anthony Naiboa, a 20-year-old man authorities described as having "mild autism," was killed on Oct. 19 after taking the wrong bus home from work, according to police.

Early Tuesday, Robert Felton, 60, was shot to death from behind in the Seminole Heights neighborhood. Investigators consider Felton to be a fourth victim in the series of murders.

“We are treating it as though it is related until we rule otherwise,” Dugan told reporters Tuesday morning.

The suspect in Felton's shooting has been described by witnesses as a tall, slim black man with a light complexion, clad in all black clothing and armed with a large black pistol, according to police.

Investigators are not calling the suspect a serial killer because they can't yet determine whether the same individual committed all the killings. Still, Dugan said police are "pretty convinced" that the suspect was involved in the deaths of at least Mitchell and Felton.

"Finding this killer is a community effort," Tampa Mayor Bob Buckhorn said in a statement Thursday. "We need to and will find who's committing these heinous, senseless murders and when we do, it will be because of people like Richard, the Seminole Heights community, Tampa Police Department and our partners in the law enforcement community who have poured their blood, sweat and tears into bringing this killer to justice."

ABC News' Julia Jacobo and M.L. Nestel contributed to this report.