A 66-year-old immigrant farm worker was formally charged with premeditated murder on Wednesday in the fatal shooting of seven co-workers near San Francisco, the second of two gun rampages in California in recent days in which 18 people were killed.

Chunli Zhao, a Chinese citizen and the lone suspect in Monday's massacre at two mushroom farms in the seaside town of Half Moon Bay, was formally presented with seven counts of murder and a single count of attempted murder during his first court appearance in nearby Redwood City.

Zhao, wearing red-colored jail garb and enclosed behind a glass panel, was ordered held without bond during a brief hearing before a San Mateo County Superior Court judge. The pudgy defendant, with close-cropped gray hair, was expressionless through the hearing. He was assigned two private defense lawyers; no plea was entered.

The next court proceeding in the case was set for Feb. 16.

A Mandarin-language translator was provided for the defendant, who according to District Attorney Steve Wagstaffe is a Chinese citizen who has lived in the United States for at least 10 years

After the hearing, Wagstaffe told reporters outside the courthouse that prosecutors have not yet determined Zhao's precise immigration status, or whether he entered the country legally.

The prosecutor said authorities do have an idea about the suspect's motives but declined to share any details. Wagstaffe also revealed the existence of one clue, saying a note was found inside Zhao's car, though he declined to disclose what it said.

The district attorney said Zhao was "cooperative" when initially interviewed by authorities following his arrest and gave "a complete statement."

Still, the expectation is that Zhao will enter a not-guilty plea as the proceedings progress, "and we want to make sure this man gets a fair trial," Wagstaffe said.

In addition to eight felony counts, the 10-page criminal complaint alleges "special circumstances," accusing Zhao of "personally and intentionally" shooting to kill.

Under California law, defendants convicted of murder with "special circumstances" can be eligible for the death penalty, though Governor Gavin Newsom in 2019 declared a moratorium on executions. The state has not put a condemned inmate to death since 2006.

Otherwise, the maximum sentence is life in prison without the possibility of parole, Wagstaffe said.

Late on Wednesday, Vice President Kamala Harris paid a condolence visit to the Los Angeles suburb of Monterey Park, where 11 people were killed in a separate rampage at a ballroom dance hall on Saturday night by a gunman who later took his own life.

Harris, a California native, laid flowers at a memorial set up outside the dance studio, and in brief comments to reporters called for Congress to enact tougher national gun-safety measures. She then met privately with victims' families.

NOT A 'COPY CAT'

California's firearm laws are among the strictest in the country, and the two shootings, coming in quick succession, left the state reeling from one of the bloodiest spates of mass gun violence in decades

Authorities said each of the two killing sprees represented the single greatest loss of life from a single act of violence in Los Angeles and San Mateo counties.

Asked if investigators believed the Half Moon Bay killings were a "copy-cat" crime inspired by the shootings in Monterey Park two days earlier, Wagstaffe said flatly, "No."

Zhao was taken into custody on Monday evening outside a sheriff's station, where police said he had driven shortly after the attack on farm workers.

The precise motive for the shooting remained unclear. Zhao had been employed by one of the growers, Mountain Mushroom Farm, and had resided at the property along with some other employees, according to its owners. Authorities said early evidence indicated the bloodshed stemmed from a workplace grievance. The second crime scene, Concord Farms, is about a mile away.

Sheriff Christina Corpus said in a CNN interview that the gunman "went after and pursued" specific victims, even though he had the chance to hurt others and that he was a "co-worker or former co-worker" of the victims at both shooting sites.

She said Zhao was not known to law enforcement before Monday's bloodshed. CNN and other media outlets have reported Zhao was the subject of a temporary restraining order after a former co-worker accused him of attacking and threatening him in 2013.

Half Moon Bay, a town of 12,000 residents south of San Francisco, is home to both a luxury resort and a low-income farming community. The shooting cast a renewed spotlight on hardships faced by the area's farm workers, many of them immigrants from Latin America and Asia who often live in labor encampments and toil long hours under poor conditions for extremely low pay.

The killings there unfolded two days after a gunman 380 miles to the south opened fire at the Star Ballroom Dance Studio, a club frequented mostly by older patrons of Asian descent in Monterey Park.

In addition to the 11 people killed, nine were wounded in Saturday night's gunfire, which some survivors and bystanders said they initially mistook for fireworks as the predominantly Asian-American community was celebrating the Lunar New Year.

Authorities said the assailant, Huu Can Tran, 72, drove a short time later to a second dance hall, where that club's operator disarmed him before he could open fire.

The next morning, Tran shot himself to death behind the wheel of his vehicle as police closed in on him south of Los Angeles.

Although his motive remained unclear, Tran was a known regular of the Star Ballroom. A tenant of a Los Angeles-rental property he owned suggested that Tran may have been nursing a grudge against other patrons.

Both rampages were notable for the suspects' age, much older than typical in deadly mass shootings that have grown all too commonplace in the United States.

Authorities said both gunmen used a semi-automatic pistols.