(CNN) — Authorities in California’s Central Valley are investigating what they believe is a series of killings that has claimed the lives of six people since last year.

Police in Stockton are offering a $125,000 reward for any information regarding the homicides, which began in April 2021 with the most recent killing reported late last month, officials said.

Seven people have been shot and one survived. They were all alone during evening or early morning hours when they were attacked, police said.

There is ballistic evidence connecting the attacks, Stockton Police Chief Stanley McFadden has said, but he didn’t elaborate on what the evidence is.

“By definition, these shootings are a series of killings, so we do believe we could have a potential serial killer, that’s how we are going to treat it, as such,” the chief said.

Now, police are asking for the public’s help in identifying a person of interest, whose image was caught on surveillance video.

“Please do not fall victim, be alert, have your head on a swivel, stay where it’s lit, communicate,” McFadden said. “We need you, we need your help, we need your tips, and we need you to help not to spread misinformation.”

The victims

The first in the string of homicides is believed to have happened during the early hours of April 10, 2021, when a 40-year-old Hispanic man was shot to death in Oakland, California, Stockton Police said in a statement Monday night.

Then on April 16, 2021, a 46-year-old Black woman was shot in Stockton and survived her injuries.

The rest of the shootings have happened this year between July and September, officials said. Four of those killed this year were Hispanic men ranging from 21 to 54 years old, and the fifth was a 35-year-old White man, police said.

On Monday, San Joaquin County’s Office of the Medical Examiner identified the victims of this year’s killings as: Paul Yaw, 35, killed on July 8; Salvador Debudey Jr., 43, killed on August 11; Jonathan Hernandez Rodriguez, 21, killed on August 30; Juan Cruz, 52, killed on September 21; and Lawrence Lopez Sr., 54, killed on September 27.

Authorities don’t know how many suspects carried out the killings

As investigators continue their probe in the case, they’re emphasizing that they’re not sure whether the killings were carried out by one person or multiple people, McFadden said.

“At this time, we don’t know if it is a person or persons. As I said before, we have absolutely no evidence that connects a person or persons to any of these incidents,” McFadden said.

He noted the killings did not appear to be related to robberies.

“They’re not talking about any gang activity in the area or anything,” McFadden said. “It’s just element of surprise.”

Suspect or suspects surveyed crime scenes before attacking

Besides the ballistic evidence connecting the string of shootings, the circumstances of each attack also show some similarities.

All seven shootings happened in dark areas where not many cameras were present. The victims were “alone, often caught off guard, or maybe relaxing in a vehicle or walking alone in almost pitch darkness,” McFadden told CNN’s Kasie Hunt Tuesday.

Further, police believe the suspected shooter or shooters may have conducted reconnaissance during daylight hours before attacking at night, according to McFadden.

“We believe that perhaps this individual, or individuals, may be looking for their area during daylight to anticipate where cameras may be, and what would be the best approach,” McFadden said.

Surveillance video shows a ‘person of interest’

The woman who survived described the suspect’s height between 5’10” and 6′ and said they wore dark clothing and a dark Covid-style mask, according to McFadden.

Stockton Police on Tuesday released surveillance video showing what they say is a “person of interest” in the killings. The video does not show the person committing any crimes on camera, police said.

The person in the video demonstrates a specific, uneven stride and upright posture, making them identifiable in the video surveillance police recovered, McFadden noted.

Motive is unclear

At this point in the investigation, authorities have not identified a motive for the killings. They have said, however, that the assailant or assailants appear to be “mission-motivated,” and there is no evidence at this time to suggest the homicides are hate crimes.

It’s also unclear whether the suspect or suspects targeted the victims, officials said.

CNN Law Enforcement Analyst John Miller noted gaps in time between shootings mean a killer may “be mature and somewhat patient.”

“Given past cases and offender characteristics, it is likely that he goes ‘hunting’ much more often than he kills,” Miller said.

“He likely ‘hunts’ regularly and strikes when everything is just right: single victim, no witnesses in the immediate area, likely an area without video coverage.”

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