As authorities continue their investigations into both tragedies, indy100 has pieced together everything we know about them so far.
Half Moon Bay
At around 2.20pm local time on Monday, the costal town of Half Moon Bay became the scene of a deadly rampage on groups of farm workers.
The shootings, which occurred at two separate locations, about a mile apart, left seven people dead and one critically wounded. The victims are all understood to be Chinese-American farm workers.
Officers found four people dead and a fifth victim with life-threatening wounds at the first location, then found three more dead at another place nearby.
The suspect, identified as Chunli Zhao, 67, was arrested after he was found sitting in his car, parked outside a sheriff's station, apparently attempting to turn himself in.
A semi-automatic handgun was found in his car, San Mateo County Sheriff Christina Corpus told an evening news conference.
She said that whilst his motive for the killings had not yet been established, he was "fully cooperating" with investigators.
Police lead away the suspect in the Half Moon Bay shootingsReuters
Corpus also confirmed that he had worked at one of the two crime scenes, describing the sites as agricultural "nurseries," where some of the workers also lived. Local media reported one site was a mushroom farm.
In a separate Bay-area incident on Monday evening that drew far less attention, one person was killed and seven wounded in a "shooting between several individuals" in Oakland, police reported, in circumstances suggesting a case of gang violence. Police gave few details, but said the surviving victims had all gotten themselves to area hospitals.
California’s Governor Gavin Newsom said he was visiting Monterey Park victims in hospital when he was called away and informed of the shootings Half Moon Bay, about 380 miles (610 km) to the north.
He tweeted in response: "Tragedy upon tragedy.”
\u201cAt 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.\n\nTragedy upon tragedy.\u201d
News of the Half Moon Bay massacre surfaced as police worked through a second full day of their investigation into the shooting in Monterey Park, just east of downtown Los Angeles.
There, a gunman shot 11 people to death and wounded nine others at the Star Ballroom Dance Studio. All of the victims are believed to be aged over 50.
Authorities said the suspect, Huu Can Tran, 72, subsequently drove to a neighbouring town and barged into a second dance hall but was confronted by the club's operator, who wrestled the weapon away during a brief scuffle.
Tran, himself a longtime patron of the Star Ballroom, catering mainly to older dance enthusiasts, fled again and vanished overnight.
He shot himself to death in his parked getaway vehicle, a cargo van, on Sunday morning, about 12 hours after his rampage, as police surrounded him in the town of Torrance, south of LA, authorities said.
Attesting to the firepower unleashed at the Monterey Park ballroom, investigators collected 42 bullet casings and a large-capacity ammunition magazine from the scene, Los Angeles County Sheriff Robert Luna told reporters on Monday.
He said a search of the suspect's mobile home in a gated senior-living community in the town of Hemet, 80 miles east of LA, turned up a rifle, electronic devices and items "that lead us to believe the suspect was manufacturing homemade" weapons silencers. Police also seized hundreds of rounds of ammunition from the dwelling and a handgun from the suspect's vehicle.
Saturday's violence unfolded in the midst of a Chinese Lunar New Year celebration in Monterey Park, a hub of the Asian-American community in Southern California, giving rise initially to concerns the attack may have been racially motivated.
However, Monterey Park Police Chief Scott Wiese said investigators were looking into unconfirmed reports that the violence may have been sparked by jealousy or relationship issues.
On Monday, Hemet Police revealed that Tran was paranoid that his family had tried to poison him decades ago and had gone to police with the allegations just weeks before his shooting rampage.
Tran visited the police department twice in early January – once on 7 January and then again on 9 January – “alleging past fraud, theft, and poisoning allegations involving his family in the Los Angeles area 10 to 20 years ago”.
The gunman told police he would return with documentation to prove his allegations but never did.
CCTV footage of the suspect Los Angeles County Sheriff's Department via AP
Elsewhere, Adam Hood, who rented a home from Tran in the Los Angeles area, told Reuters his landlord enjoyed ballroom dancing and was a regular at the Star Ballroom, though he complained that others there were talking behind his back.
"He was distrustful of the people at the studio, angry and distrustful. I think he just had enough," Hood said.
Deadliest mass shootings in the area
The Monterey Park attack now ranks as the deadliest mass shooting ever in Los Angeles County, according to Hilda Solis, a member of the county Board of Supervisors.
By comparison, the 1984 massacre of 21 people at a McDonald's restaurant in San Diego stands as the greatest loss of life from a single shooting incident on record in California.
Fourteen people were slain in San Bernardino, east of L.A. County, in 2015, by a married couple who authorities described as extremists inspired by foreign terror groups. They were killed hours later in a shootout with police.
What’s unusual about the two latest atrocities?
The Half Moon Bay and Monterey Park shootings are notable for the age of the suspects, one in his late 60s, another in his early 70s.
A database of 185 mass shootings between 1966 and 2022 maintained by the nonprofit Violence Project includes just one carried out by someone 70 or older - a retired miner who killed five people in Kentucky in 1981.
Mourners held a candlelit vigil for the Monterey Park victimsGetty Images
Is anything being done to tackle gun violence in the country?
On Monday, Joe Biden implored lawmakers in Congress to pass a pair of bills seeking to ban assault weapons and high-capacity magazines and raise the purchasing age to 21, CNNreported.
“The majority of the American people agree with this common sense action. There can be no greater responsibility than to do all we can to ensure the safety of our children, our communities, and our nation,” the president said in a statement.
A day earlier, before the Half Moon Bay killing spree, Vice President Kamala Harris spoke of the Monterey Park tragedy.
She told a crowd in Tallahassee, Florida: “Yet another community has been torn apart by senseless gun violence. All of us in this room and in our country understand this violence must stop.”
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