Stockton, California - A series of fatal shootings in California are now believed to be interconnected, according to the Stockton Police Department.

Police are searching for a person of interest amid the investigation into six shootings that occurred between July and September. Investigators told ABC News that there is physical evidence linking the crime scenes.

All killings occurred at night or in the early morning. The victims, all of whom were men, were each alone at the time of the shooting.

Police do not believe that the attacks are gang-related, hate crimes, or specifically targeting homeless individuals. While four of the victims were Latino, one was a white man.

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Stockton Police Chief Stanley McFadden confirmed that the attacks were not robberies either. "It's just element of surprise," he said.

"By definition, you could probably very well call this serial killings," McFadden said.

The victims of the fatal shootings were identified by the San Joaquin County's Office of the Medical Examiner on Monday.

On July 8, 35-year-old Paul Yaw was killed. Three days later, Salvador Debudey Jr. (43) followed, with 21-year-old Jonathan Hernandez Rodriguez fatally shot on August 30. Juan Cruz (52) died on September 21, and 54-year-old Lawrence Lopez Sr. was killed six days after that.

Two other shootings from April 2021 are now suspected by police to be connected as well. While one of the victims – a 46-year-old woman – survived her injuries, a 40-year-old man shot on April 16 did not.

A grainy photo of a person of interest in the case, who appeared in videos from multiple crime scenes, was shared by police on Sunday.

The Stockton Police Department is offering a $95,000 reward for information leading to an arrest in the investigation.