The slayings of seven people, gunned down in a small Northern California city, was an act of "workplace violence" that victimized members of the "migrant community," officials said Tuesday.
Suspect Chunli Zhao, a 66-year-old resident of Half Moon Bay, worked at Mountain Mushroom Farm, one of two agricultural businesses where workers were killed on Monday afternoon, authorities said.
"The only known connection between the victims and the suspect is that they may have been co-workers," San Mateo County Sheriff Christina Corpus told reporters in nearby Redwood City. "All of the evidence we have points to this being the instance of workplace violence."
Zhao was arrested in the parking lot of a sheriff's substation in Half Moon Bay shortly after the attacks.
"The semi-automatic handgun was legally purchased and owned," Corpus said.
Sheriff's investigators also said they're struggling to notify loved ones of victims who were described as "members of the migrant community," who were of Asian and Hispanic descent.
"As some of these victims were members of our migrant community, this represents a unique challenge when it comes to notifications (of survivors) and identifications," Corpus said.
While investigators did not immediately disclose what, if any, criminal record Zhao might have, it didn't rise to any level of significant concern, officials said.
"I will say there were no specific indicators that would have led us to believe that he was capable of something like this and he was not known to us," sheriff's Capt. Eamonn Allen said.
Zhao, who investigators had originally said was 67, is scheduled to make his first court appearance on Wednesday afternoon.
District Attorney Steve Wagstaffe called Monday's attack the worst in San Mateo County history.
"We've never had one in this county of this many deaths ... at one time," the prosecutor said. "So it's a very hectic scene."
"Jill and I are praying for those killed and injured in the latest tragic shooting in Half Moon Bay, California," President Joe Biden said in a White House statement issued Tuesday. "For the second time in recent days, California communities are mourning the loss of loved ones in a senseless act of gun violence."
The Half Moon Bay slayings were in the middle of a horrific 72-hour period of gun violence across California and the nation.
A man in Monterey Park, an Asian-majority suburb of Los Angeles, gunned down 11 people at a Lunar New Year dance party late Saturday night, authorities said.
A dozen people were wounded early Sunday morning when gunfire erupted in a Baton Rouge, Louisiana, bar, police said.
Two students, 18 and 16, were gunned down Monday afternoon at a charter school in Des Moines, Iowa, that's tailored for disadvantaged youths and has close ties to police, authorities said. An 18-year-old was arrested and faces two counts of murder.
Less than five hours after the Half Moon Bay shootings began, gunfire erupted 40 miles away in Oakland where one person was killed and seven were injured, police said.
Three people were gunned down early Tuesday morning in Yakima, Washington, officials said. A 21-year-old man is being sought in connection to the 3:30 a.m. PT gunfire at a Circle K convenience store.
This article was originally published on NBCNews.com