Police in Stockton, California, are searching for a person of interest in a series of deadly, after-dark shootings in the city.
Police said that an unidentified person captured on grainy security video could be a suspect or a witness and that others may be involved in the five attacks that have happened since July.
"We have a series of homicides that we believe are interconnected," Stockton Police Chief Stanley McFadden said at a news conference Friday. "By definition, you could probably very well call this serial killings."
He said police have ruled out gang violence, hate crime and the targeting of homeless residents. One of the five victims is a white man - the others are Latino, and not all were unhoused, McFadden said.
Detectives haven't been able to determine if there is one shooter or possibly more, the chief said.
He said all of the slayings have happened after dark and in shaded areas with few security cameras. Each of the attacks has involved a single victim.
"It wasn't a robbery," he said. "Items aren't being stolen. They're not talking about any gang activity in the area or anything. It's just, element of surprise."
The attacks began in July and have happened as recently as this week, according to police, who describe them this way:
On July 8, an unidentified, 35-year-old man described only as white was fatally shot. It was reported at 12:31 a.m.
On Aug. 11, an unidentified 43-year-old man described as "Hispanic" was killed at 9:49 p.m.
On Aug. 30, an unidentified 21-year-old man described as "Hispanic" was fatally shot at 6:41 a.m.
On Sept. 21, an unidentified 52-year-old man described as "Hispanic" was killed at 4:27 a.m.
On Tuesday, an unidentified, 54-year-old man described as "Hispanic" was fatally shot about 1:50 a.m.
The city is offering a $75,000 reward for information leading to an arrest, and an additional $10,000 was put up by Stockton Crime Stoppers.
Whoever's shooting appears to be creeping in the shadows, the chief said. "The areas are dimly lit, they're overshadowed by trees," McFadden said.
"Be alert," he said. "Have your head on a swivel."
He also asked residents to be alert online and avoid spreading disinformation.
"All that does is create additional challenges for the investigators," McFadden said.
This article was originally published on NBCNews.com