At least two of the suspected gunmen carried out the attacks using semi-automatic weapons and at least one of the guns was currently illegal to own in the state.
The following Q&A has been lightly edited for clarity and brevity.
Monterey Park: 11 dead, gunman dead
The gun used in the attack was a MAC-10 semi-automatic assault weapon or a Cobray M11, according to authorities (they’ve said both). What does that mean and is that kind of gun legal in California?
JM: First, a caveat: An original MAC-10 – the Military Armament Corporation Model 10 – is typically a fully automatic submachine gun. That means several bullets are ejected per trigger pull.
Machine guns are heavily regulated under the National Firearms Act. The gun he used was not a machine gun. MAC-10 variants include the Cobray M11/9, which was originally reported as having been wrestled away from the gunman.
MAC-10 variants are illegal under California’s assault weapons ban for two reasons: They have a threaded barrel, and they’re designed to take 30-round magazines. Anything over 10 rounds is illegal under California law.
SG: The gun that was wrestled away from him appears to have had a suppressor/silencer attached to it, which means it likely had a threaded barrel which would make it illegal to purchase today.
It is also not legal to purchase today because California has banned the sale of handguns without certain features, such as a magazine safety, loaded chamber indicator, or “microstamping” technology (which no gun company actually produces).
However, the suspect in this case is 72 years old and the ATF trace indicates he bought the gun himself. We need more information about when the purchase was made. But, given the company who made it went out of business in the 1990s, it’s possible he legally bought it before California’s “assault weapons” ban went into effect.
Were any modifications made to the gun? If so, did that make it more dangerous and/or illegal?
SG: CNN’s reporting suggests police believe he was illegally making suppressors, also known as silencers, at home. The video of him being disarmed by Brandon Tsay shows what appears to be a suppressor attached to the end of the barrel. California … has a total ban on even possession of suppressors. So, it was not legal for him to have.
Silencers reduce the sound of gunfire. However, they do not actually make a gunshot silent. Depending on the caliber and effectiveness of the suppressor, they generally lower the sound to the same decibel level as a jackhammer. Suppressors work exactly the same way that car mufflers do and were invented by the same person (Hiram Percy Maxim).
How was he able to fire off so many rounds?
SG: Police report the shooter used a 30 round magazine, which California also bans new sales of. Given the suspect’s age, he also could have purchased the magazine before California instituted its ban several decades ago.
California passed a confiscatory law outlawing possession of magazines that hold more than 10 rounds back in 2016. However, a federal judge blocked enforcement of it over concerns it violates the Constitution and that case (Duncan v. Beccera) is still working its way through the courts.
Additionally, survivors report he also reloaded during the attack. So, the magazine’s size did not prevent him from having to reload his gun at least once.
Also, the gun he used can fire rounds at basically the same rate as any other semi-automatic (one shot per each trigger pull) firearm.
The gun had a long barrel at the end of it – what is that and what does it do?
JM: I believe this is a silencer which muffles the sound of a gunshot. But that hasn’t been confirmed by law enforcement. Silencers are regulated under the same federal law that regulates machine guns. He would have had to register the device with the federal government to legally own it.
Half Moon Bay: 7 dead, gunman in custody
Authorities have said the gun was a semi-automatic weapon, legally registered to the shooter. How is this gun different from the semi-automatic used in the Monterey Park shooting and why is it legal and the other one isn’t?
JM: The Monterey Park gun isn’t California legal because it has prohibited features under the state’s assault weapons ban: a threaded barrel, and it’s designed to take 30-round magazines.
The gun used in the Half Moon Bay shooting was a registered semi-automatic handgun that didn’t have any of the features listed under California’s assault weapons ban. Most handguns in circulation are semi-automatic, which means another bullet automatically moves into the chamber after firing. It doesn’t have to be manually cocked, like a revolver.
What does the number of victims tell you about the kind of gun used?
JM: AR-15s are particularly deadly, so they leave fewer survivors, but most mass shootings are actually perpetrated with handguns. The Half Moon Bay shooting was so deadly probably because he targeted his victims and shot them at close range.
With the Monterey Park shooting, I knew immediately that the gunman didn’t use an AR-15 because there were so many survivors. A MAC-10 variant and other “assault pistols” are closer in lethality and functionality to a handgun than an AR-15. They’re old guns, heavy and not terribly accurate, so the death toll resembled a handgun rampage more than an assault rifle rampage.
SG: Unfortunately, when an armed person attacks a group of unsuspecting and unarmed people, it doesn’t not take any kind of advanced weaponry or tactics to inflict a horrible toll on a community. Mass killings have been carried out with all sorts of weapons from semi-automatic rifles and handguns to pump-action shotguns, to bolt-action rifles, to knives or blunt instruments.
Oakland: 1 dead, gunman on the loose
So far, cops have not found a weapon, just shell casings. Can they trace the kind of weapon using those casings and/or the victim’s wounds?
JM: Shell casings can be run through NIBIN, the ATF’s ballistics database, to connect it to shell casings found at other shooting scenes. But NIBIN doesn’t produce a gun’s serial number or chain of custody. It can connect shooters across jurisdictions though, and stop repeat shooters from striking again.
SG: The police can identify what caliber of weapon was used in the attack from casings recovered at the scene or from victims’ wounds. However, it is much more difficult to determine the specific firearm used in an attack from spend shell casings or wounds alone.