Five deaths of men walking alone on roads in Stockton at night or in the pre-dawn hours in the last several months appear to be linked, and Stockton police now say they are on the hunt for a serial killer.

The first killing happened on just after midnight, on the morning of July 8. As ABC News reports, 35-year-old Paul Alexander Yaw was killed at 12:31 a.m. on the 5600 block of Kermit Lane in Stockton.

Yaw's family put out a statement to ABC News confirming his death, and saying, "He was a good boy who grew into a good man with a big heart. He will always live on in our hearts. He was always there for you if you needed him. He was a son, brother, father, grandson, nephew and cousin. I still can't believe he's not coming back. I hope this helps to catch the person(s) responsible."

Subsequent shootings followed in August and September, with the most recent occurring just last week. All of the other victims besides Yaw have been Hispanic males.

Sacramento affiliate KXTV reports that the City of Stockton is now offering a $75,000 reward for information leading to an arrest and conviction in the case, and CrimeStoppers is offering an additional $10,000 reward. They have also revealed a shadowy photograph of what appears to be a man from behind, whom police say is a person of interest in the case.

The other shootings occurred on August 11, when a 43-year-old man was fatally shot at 9:49 p.m. on the 4900 block of West Lane.; a 21-year-old man was fatally shot at 6:41 a.m. on August 30 on the 800 block of E. Hammer Lane; a 52-year-old man was fatally shot at 4:27 a.m. on September 21 on the 4400 block of Manchester Avenue.; and a 54-year-old man fatally shot at 1:53 a.m. on Sept. 27 on the 900 block of Porter Avenue.

The victim in the latter shooting has been identified by family to KXTV as Lorenzo Lopez. His brother, Jerry Lopez, tells the station, "He was just a person who was out here at the wrong place at the wrong time at the wrong circumstance. It’s hard to process that this has happened. I mean me and my brother have been like twins. We were a year a part so we were pretty close."

As recently as last week, after the shooting of Lopez, police were still treating the five shooting incidents as random and unrelated, but they now say they have physical evidence linking all four crimes. And all five shootings took place in the same five-mile radius of one another.

Stockton Police Chief Stanley McFadden wrote on Facebook about the case on Friday, saying that misinformation is being spread around town and "I know there are many sources out there that are talking about this investigation."

Police are encouraging people not to walk alone at night, and to stick to well-lit areas if you do.

Anyone with information on the case is being asked to call 209-937-8167, or you can also email your information to [email protected].

"If anyone, has information regarding these investigations, call us immediately," McFadden writes. "Please remember our victims have grieving family members who need resolution."