Workplace violence is believed to be the motive for a gunman who opened fire at two Northern California farms on Monday, killing seven and injuring one, authorities said.

All victims -- six men and two women -- were adults, authorities said. The victims were of Asian and Hispanic descent, authorities said.

The suspect’s semi-automatic handgun was legally purchased, authorities said.

The suspect, 67-year-old Chunli Zhao, worked at one of the shooting locations, Mountain Mushroom Farm, but it's unclear what connection he may have had with the victims beyond being co-workers, authorities said.

Zhao was not known to police, according to authorities.

Zhao is expected to be arraigned on Wednesday. Prosecutors will review the case and decide on charges, officials said.

The coroner's office is working to notify the victims' next of kin, but authorities said it's difficult to reach families because some victims are migrants.

-ABC News' Alex Stone

President Joe Biden released a statement on Tuesday in the wake of the deadly mass shootings in Half Moon Bay and Monterey Park, California.

"Jill and I are praying for those killed and injured in the latest tragic shooting in Half Moon Bay, California," Biden said. "For the second time in recent days, California communities are mourning the loss of loved ones in a senseless act of gun violence."

"Following a briefing from my homeland security team, I have directed my administration to ensure local authorities and the broader Half Moon Bay community have the full support of the federal government in the wake of this heinous attack," the president added.

On Monday, two days after another deadly mass shooting in Monterey Park, Sens. Dianne Feinstein, D-Calif., Richard Blumenthal, D-Conn., and Chris Murphy, D-Conn., reintroduced a federal ban on assault weapons as well as legislation that would raise the minimum purchase age to 21. In his statement on Tuesday, Biden said that while “we await further details on these shootings, we know the scourge of gun violence across America requires stronger action.”

"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," the president said.

Aaron Tung, principal at Concord Farms, one of the locations where the shooting took place, said the company wanted to thank the community for the "outpouring of thoughts and support."

"We thank law enforcement for their swift response and actions. Concord Farms is a family owned and operated mushroom farm at this location for 37 years," he said in a statement.

Tung added, "With no past knowledge with this gunman or his motives, we are shook and very eager to gain more information from the authorities and their investigations. Our hearts are with the victims, their families and the Chinese American community—from Half Moon Bay to Monterey Park."

-ABC News' Abigail Shalawylo

San Mateo County Sheriff Christina Corpus said a semi-automatic handgun was found in the suspect's car.

The suspect, 67-year-old Chunli Zhao, is cooperating and being interviewed, the sheriff said.

Zhao is believed to have acted alone, Corpus said.

-ABC News' Marilyn Heck and Abigail Shalawylo