Last June, alleged Buffalo supermarket mass shooter Payton Gendron, then 17, threatened to shoot up his school.

Students at Susquehanna Valley High School in Conklin, NY, had been asked about their plans after graduation and Gendron said he wanted to commit a murder-suicide.

“A school official reported that this very troubled young man had made statements indicating that he wanted to do a shooting, either at a graduation ceremony, or sometime after,” a government official revealed to the Buffalo News.

Gendron’s threat was so disturbing that the school reported it to local Broome County police, who, after interviewing him, brought him in for a mental health evaluation.

He spent two days in a hospital and was released.

At the time, the Washington Post has reported, Gendron owned a Savage Axis XP rifle that he received from his father as a Christmas present in December 2019, when he was 16.

In December 2021, he purchased a Mossberg 500 shotgun.

In January this year, he bought a used Bushmaster XM-15 semi-automatic rifle.

And on Saturday, according to authorities, he took all three guns to a Tops Friendly Markets store in Buffalo and used the Bushmaster to shoot 13 people, leaving 10 of them dead.

Gendron, now 18, was an internet-radicalized white supremacist who hated black people and wanted to kill as many of them as possible. (Eleven of the 13 victims were black.)

In a repellent “manifesto” that he pre-emptively wrote to explain his murderous rampage, Gendron said he illegally modified the Bushmaster with his father’s power drill so he could use 30-round magazines and wouldn’t have to reload so frequently.

Gendron mocked the New York state gun laws as “cuck” and those who follow them as “cucked.”

The laws allow customers over 18 to buy guns, though they need to pass a criminal background check at the time of the sale, which Gendron did.

These background checks are supposed to red-flag individuals with a history of mental illness, but that only shows up if they were institutionalized by a judge, which he wasn’t.

Yet there were other clues to his mental instability.

Two of Gendron’s former classmates told the New York Times that he showed up in class wearing hazmat gear after pandemic restrictions were lifted in 2020.

“He wore the entire suit, boots, gloves, everything,” said Nathan Twitchell, 19. “Everyone was just staring at him.”

Gendron didn’t return to school much after that, preferring online coursework, and becoming more reclusive.

His “manifesto” details how the isolated teen disappeared down a sick, twisted online rabbit hole of insane conspiracy theories and vile racism.

Inevitably, a partisan point-scoring blame game has erupted over who inspired him to do what he did, but as journalist Glenn Greenwald brilliantly illustrates in a lengthy new Substack article, “all ideologies spawn psychopaths who kill innocents in its name.”

The truth is that this psycho seems to have hated everyone, on all sides of the political divide.

And the real question in the wake of this latest sickening horror is what to do to stop more attacks like it?

I’m not going to shout about gun control again.

I’ve tried that after all the worst US mass shootings over the past decade, and it has invariably failed to make one iota of difference to the debate.

As Jay Leno once told me: “Americans don’t like being told they have to give up their guns, Piers, especially by someone with your accent.”

I get that.

Guns are part of US culture.

If an American came to Britain and furiously demanded we give up cricket because it’s too dangerous (numerous people, including an international star several years ago, have been killed playing it), we’d run them out of town, just as unhinged radio shock jock Alex Jones tried, unsuccessfully, to have me deported after I vented my wrath about guns on CNN after Sandy Hook.

I know that many Americans believe passionately in their constitutional right to bear arms, a right endorsed by the Supreme Court in 2008.

I also know that those same Americans have an extreme aversion to the words “gun control.”

So why don’t we try a different phrase: “gun safety.”

How do you make a country awash with over 300 million guns safer from gun violence?

After all, New York state has some of the most restrictive gun laws in the country, and New York City’s laws are even tougher.

But it didn’t stop Gendron because he thought the laws were “cuck.”

All criminals think that.

That’s why they’re criminals.

So, while I may find it crazy that Gendron can’t legally buy an alcoholic drink for another three years, until he turns 21, or a Kinder Surprise chocolate egg because they’re banned in the US due to the risk of choking on the little toys contained inside, but he was able to legally buy a semi-automatic rifle at just 18, it’s clear that new laws alone won’t stop gun violence, though I believe they would help curb it.

What should not be up for debate is that the best way to stop bigoted lunatics like Gendron from committing heinous crimes is to act when they wave obvious red flags.

He was self-evidently a lethal cocktail waiting to explode, but the system failed to stop him because, we’re absurdly told, he wasn’t on anyone’s “radar.”

Buffalo Police Commissioner Joseph Gramaglia said Gendron had no further contact with law enforcement after his release from the hospital.

“Nobody called in,” he said. “Nobody called any complaints.”

To which my response is, why the hell weren’t YOU calling into HIM, Commissioner?

He most definitely was on your radar, as a potential mass shooter, but you just let him drop off.

New York Gov. Kathy Hochul, a Buffalo native, told ABC News after launching an investigation into the shooting: “I want to know what people knew, and when they knew it.”

That probe will rightly include social media platforms like Twitch, on which Gendron livestreamed his massacre (it was taken down after 2 minutes). How much did it help fuel his sick mindset?

But right now, there are urgent questions I would like Broome County police to answer:

Did you check Gendron’s computer and phone after he threatened to shoot up his school? We know he spent many months, possibly years, studying previous mass shootings and race hate crimes.

Did you speak to his schoolmates and ask them about his worrying behavior and state of mind that was causing them concern?

Did you know his father had given him a gun for his 16th birthday?

Why didn’t you put any note on his background check files detailing his threat to shoot up his school and subsequent two-day mental health evaluation? The man who sold him the Bushmaster, Robert Donald of Vintage Firearms in Endicott, NY, says nothing showed up to give him any doubts about whether to sell. “He didn’t stand out,” Donald told police. “Because if he did, I would’ve never sold him the gun.”

Surely, whatever your view of guns, we can all agree it’s bonkers that an obviously troubled teenager known to police for threatening to enact a mass shooting was then left alone to legally arm himself and commit a mass shooting less than a year later.

As Maya Angelou said: “When people show you who they are, believe them the first time.”