Officials in both states were trying to determine if the killer may be linked to a string of 2018 murders in Rogers Park, based on similarities in surveillance videos from both locations.
However, Stockton police said later Friday there did not appear to be a connection.
In 2018, two men were shot and killed in Chicago's North Side Rogers Park neighborhood by the same suspect just days apart.
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Douglas Watts, 73, was walking his dogs when he was shot by the masked suspect.
The same suspect murdered Eliyahu Moscowitz, as he walked the path in Loyola Park.
SEE MORE: Rogers Park shootings still unsolved after 2 years, killer still at large
In both cases, the killer approached from behind and shot them in the head.
The suspect also had a very distinct "duck walk" and upright posture, which had drawn the attention of the Stockton Police Department.
Police there said tips came in showing them the news videos from Chicago of the suspected "Duck Walk Killer."
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The way both people walked had them looking to see if it was the same person.
"During this investigation, we have reached out to numerous agencies in our state and across the nation including Chicago," said Joe Silva, with Stockton police.
Stockton police have linked seven recent shootings to their possible serial killer.
SEE ALSO: Police search for apparent serial killer tied to 6 murders in California, victims' IDs released
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All but one of those shootings were fatal.
Stockton police told ABC News that all of the victims were ambushed, none were robbed and none of the incidents were drug- or gang-related.
In Chicago and in Stockton, the assailant remains at large.
Alderperson Maria Hadden of Rogers Park hopes it still brings new light to the cold case.
"You never know. A person who maybe remembers something they didn't remember before or was involved in a way and didn't realize it, different connections are made so absolutely. I think that even though these don't appear to be connected that maybe something positive in solving these cases will come out of it," Hadden said.
Chicago police said both CPD and California detectives do not believe there is a connection in the cases.