(NewsNation) — The Stockton Police Department is searching for the person responsible for fatally shooting six men — five in recent months — and injuring one woman. Authorities connected the deaths through ballistics testing to two additional cases from last year — a man’s death in Oakland and the nonfatal shooting of a woman in Stockton.

The department released cloudy surveillance video of their person of interest in the series of homicides. McFadden says the person of interest was captured on many videos and that everyone in the area is at risk.

Police Chief Stanley McFadden said the series of killings had some consistency as all of them have been in very dark locations, where there are very few cameras, there’s no lighting, and there are no witnesses.

“We believe this person or persons are pre-planning these events, and, and they’re on a mission to kill. They’re catching people by surprise,” McFadden said. “We have people on foot that have fallen victim, we have people that were in their vehicle that have also fallen victim. We just really need everyone to have their eyes out, their heads on the swivel and protecting each other out there.”

McFadden said what he means by “mission to kill” is that they’ve found that no items are being taken from victims, nor are their vehicles.

“We’re finding, you know, the wallets and car keys are just where they lay on the ground. So it’s not robberies or anything. It’s just a person that is killing,” he explained.

“If you see something, say something,” he said. “I’m a firm believer that there’s someone who knows that a crime is about to be committed, and there’s someone who knows after the fact, and we need those people to come forward and help us in these investigations.”

The reward in the search for a killer linked to the six California murders has increased to $100,000.