Another murder, this one last year in the Bay Area, may be linked to a string of unsolved killings in Stockton from the last three months, as a new serial killer investigation is rattling nerves in the Central Valley.

On Monday we learned that five seemingly random shootings, all of which took place on darkened, late-night streets in Stockton since July, are looking like the work of a serial killer. Now two more shootings, one of them fatal, are being added to this shooter's list of alleged deeds.

In all the previously discussed shootings in Stockton, the most recent of which was last week, the victims were male, and four of the five were Hispanic males. Now, as the Stockton Police Department announced late Monday night, we can add another Hispanic male victim to the list, an unnamed 40-year-old man who was killed in Oakland on April 10, 2021 around 4:18 a.m.

The Alameda County Coroner’s Bureau has identified the victim as Juan Vasquez Serrano of Oakland, and he was reportedly 39 years old.

April 10, 2021 was called, at the time, "the deadliest day of 2021" in the city of Oakland, because three homicides occurred that day. This unsolved shooting death was hardly mentioned in the news coverage, as it was overshadowed by a liquor store shooting that same day that cascaded into a deadly arson that killed a man and his baby daughter. After a pandemic-driven period of relative quiet on Oakland's streets, the city saw a rapid uptick in violence last year, and by April police were investigating a new homicide every three days.

A second shooting, in which a Black woman in Stockton was injured but survived, occurred just six days later, on April 16, 2021. That took place at 3:20 a.m. at Park and Union street in Stockton, and the woman was reportedly alone at the time.

"While detectives continue to follow up on this series, detectives can confirm the following two additional cases are linked," the posting from Stockton police says.

The linkage, which could be from ballistic or other evidence, means that this potential serial killer has been active now for at least a year and a half. This person also may or may not have taken a long pause between killings — pending more unsolved, late-night shootings that may be linked as well. Police have not disclosed the nature of the evidentiary link that they have found.

The next shooting investigators have publicly discussed occurred in early July 2022, when 35-year-old Paul Alexander Yaw was killed at 12:31 a.m. on July 8 on the 5600 block of Kermit Lane. That's a lapse of 15 months.

NBC News reports that at least two of the victims, including Yaw, were homeless.

Police on Monday released a grainy image of a person, from behind, who they say may be a witness or a suspect to one of the crimes.

"It definitely meets the definition of a serial killer," said Stockton Police Officer Joseph Silva, speaking to the Associated Press. “What makes this different is the shooter is just looking for an opportunity, and unfortunately our victims were alone in a dark area.”

So far none of the victims appear to have known each other or had any connection, and neither drugs nor gang activity are suspected in any of the cases.

Anyone with information on the case is being asked to call 209-937-8167, or you can also email your information to [email protected]. Police and CrimeStoppers are offering a $95,000 total reward for information that leads to an arrest and conviction.

Previously: A Serial Killer May Have Recently Murdered Five Men In Stockton