The suspect arrested in connection with a pair of shootings in Northern California on Monday may have worked with the victims, the local sheriff said.

“All of the evidence we have points to this being the instance of workplace violence,” San Mateo County Sheriff Christina Corpus said at a press conference on Tuesday.

Seven people were killed and one was injured in the two related shootings at farms in Half Moon Bay on Monday. 

Police arrested Chunli Zhao on Monday afternoon in the parking lot of the Sheriff’s Office Half Moon Bay Police Substation, where he was found sitting in his car. Zhao worked at Mountain Mushroom Farm, the site of the first shooting, Corpus said.

Zhao, who police believe acted alone, legally purchased and owned the semi-automatic handgun found in his car, the sheriff added.

Corpus added on Tuesday that the coroner’s office is still working to identify the victims and notify next of kin. 

“As some of these victims were members of our migrant community, this represents a unique challenge when it comes to notifications and identifications of next of kin,” she said.

The deaths come on the heels of a mass shooting in Monterey Park, Calif., on Saturday night that killed 11 people. There have been at least 39 mass shootings in the U.S. so far in 2023, according to the Gun Violence Archive.

President Biden renewed his call for a federal ban on assault weapons on Tuesday in the wake of the California shootings.

“Even as we await further details on these shootings, we know the scourge of gun violence across America requires stronger action,” Biden said in a statement. “I once again urge both chambers of Congress to act quickly and deliver this Assault Weapons Ban to my desk, and take action to keep American communities, schools, workplaces, and homes safe.”