TAMPA, Fla. (WTSP) -- When the fourth victim in a string of mysterious murders was shot and killed early Tuesday morning along North Nebraska Avenue in Seminole Heights, it immediately revived concerns about a possible serial killer in the area.

All the shootings are roughly a half mile away from each other. It takes less than five minutes to get to all four locations.

Here is a timeline of each shooting:

1. Oct. 9, 2017: Tampa police say Benjamin Mitchell, 22, was shot and killed while waiting for the bus alone along 15th Street North and Frierson Avenue. It happened around 9 p.m.

2. Oct. 13, 2017: Monica Hoffa's body was found in a grassy, empty lot in the 1000 block of New Orleans Avenue on an early Friday morning. Police believe she was killed on Oct. 11. She was 32 years old. Because of how close the shootings were to each other, police became suspicious they were related.

3. Oct. 19, 2017: Just two blocks away from where Benjamin Mitchell was shot and killed, Anthony Naiboa, 20, was murdered along 15th Street North between Conover Street and Wilder Avenue. Police say they were patrolling the area because of the previous shooting and heard a gunshot around 8 p.m. They responded immediately and found Naiboa's body, but were unable to find the killer. Police said Naiboa's parents worried because he was autistic, and had not yet made it home after taking the bus.

4. Nov. 14, 2017: A little more than a month after the first victim was shot and killed, Ronald Felton, 60, was found dead at Nebraska Avenue and McBerry Street. Witnesses reported to police that Felton was crossing the street when he was shot from behind. Felton's sister said he was on his way to volunteer at a local food pantry.

On Wednesday, Tampa police released a second surveillance video of the suspect, and urged neighbors to report anything suspicious to police.

"At 4:51 a.m. on Nov. 14, was there someone you know that should've been at home, should've been at work and they weren't there? We need to know," said Tampa Police Chief Brian Dugan.

The reward for information leading to the suspect's arrest was increased on Wednesday to $91,000.

Emerald Morrow is a reporter with 10News WTSP. Like her on Facebook and follow her on Twitter. You can also email her at emorrow@wtsp.com.