An agricultural worker killed seven people at the farm where he worked and at another business in Northern California, plunging the state into mourning again in the wake of its third mass killing in eight days.

Officers arrested a suspect in Monday's shootings, 67-year-old Chunli Zhao, after they found him in his car in the parking lot of a sheriff's substation, San Mateo County Sheriff Christina Corpus said.

Seven people were found dead and an eighth wounded at a farm and another location several miles away, the Sheriff's Office said. Officials have suspected that Zhao worked at one of the facilities and that the victims were workers as well, Corpus said. Officials haven't determined a motive for the shooting.

San Mateo County Sheriff Christina Corpus confirmed Tuesday that Zhao was an employee at Mountain Mushroom Farm. She says that the only known connection between the shooter and his victims is that "they may have been coworkers."

The sheriff's office said seven of the victims were men and one was a woman. Some were Asian and others were Hispanic, and some were migrant workers.

Aerial television images Monday showed police officers collecting evidence from a farm with dozens of greenhouses, which appeared to be the location where police found four dead. On Tuesday morning, police continued to block off the location.

On Jan. 16, a teenage mother and her baby were among six people killed in a shooting at a home in California's Central Valley. Officials discussing the investigation mentioned a possible gang link to the killings.

California was still reeling Tuesday from an attack on a Lunar New Year celebration in Monterey Park that killed 11 and cast a shadow over an important holiday for many Asian-American communities. Authorities are still seeking a motive for the Saturday shooting.

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"For the second time in recent days, California communities are mourning the loss of loved ones in a senseless act of gun violence,' President Joe Biden said Tuesday morning. "Even as we await further details on these shootings, we know the scourge of gun violence across America requires stronger action."

The new year has brought six mass killings in the U.S. in fewer than three weeks, accounting for 39 deaths. Three have occurred in California since January 16, according to a database compiled by The Associated Press, USA Today and Northeastern University. The database tracks every mass killing - defined as four dead not including the offender - committed in the U.S. since 2006.

The killings occurred on the outskirts of Half Moon Bay, a city about 48 kilometers south of San Francisco.

Half Moon Bay Vice Mayor Joaquin Jimenez said the victims included Chinese and Latino farmworkers. Some workers lived at one of the facilities and children may have witnessed the shooting, she said. Corpus said it wasn't immediately clear how the two locations were connected.

Police tape is placed near the scene of a shooting, Jan. 23, 2023, in Half Moon Bay, Calif.

The Sheriff's Office first received reports of a shooting in the afternoon and found four people dead and a fifth wounded at the first scene. Officers then found three more people fatally shot nearby, Capt. Eamonn Allen said in a news release.

About two hours later, a sheriff's deputy spotted Zhao's car parked outside a sheriff's substation in a strip mall and arrested him.

A video of the arrest showed three officers approaching a parked car with drawn weapons. Zhao got out of the car, and the officers pulled him to the ground, put him in handcuffs, and led him away. A weapon was found in his vehicle, officials said. The video was captured by Kati McHugh, a Half Moon Bay resident who witnessed the arrest.

The sheriff's department believes Zhao acted alone.

"We're still trying to understand exactly what happened and why, but it's just incredibly, incredibly tragic," said state Sen. Josh Becker, who represents the area and called it "a very close-knit" agricultural community.

Half Moon Bay is a small coastal city with agricultural roots, home to about 12,000 people. The surrounding San Mateo County is a mixture of coastal cities and hills dotted with farms, included floral and tree nurseries as well as ranches. The county also allows cannabis to be grown in greenhouses and at nurseries in some areas.

It's a majority-white community. About a third of the population is Latino and about 5% is Asian, according to Census data.

"We are sickened by today's tragedy in Half Moon Bay,' said San Mateo County Supervisor Dave Pine said. "We have not even had time to grieve for those lost in the terrible shooting in Monterey Park. Gun violence must stop."

California Gov. Gavin Newsom tweeted that he was 'at the hospital meeting with victims of a mass shooting when I get pulled away to be briefed about another shooting. This time in Half Moon Bay. Tragedy upon tragedy.'