What London killer told police:

‘I’m going to be a terrorist’ ... and they still didn’t stop him

One of the three assailants in the London Bridge attack bragged, “I’m going to be a terrorist’’ when he was busted on his way to Syria last year, and even had ISIS videos with him — but he was freed and never made it onto the Brits’ radar.

Youseff Zaghba, a Moroccanborn 22-year-old, had been arrested in March 2016 while trying to travel to Syria, officials revealed Tuesday.

Zaghba was stopped in Bologna, Italy, as he was about to board a plane for Turkey with the apparent intention of joining ISIS jihadists fighting in Syria, according to Italian media.

The young Muslim had a oneway ticket and was carrying only a backpack.

“I’m going to be a terrorist,” Zaghba bragged to security staff at Bologna’s airport when asked why he was traveling to Istanbul, according to La Repubblica.

Officers then uncovered ISIS propaganda videos on his cellphone but said they never found enough evidence to prove he had links to terrorism.

Zaghba was released, and his name was placed in a Europewide database of potential terrorists, a source told The Guardian. Italian authorities also said they notified British and Moroccan security services about his status as a potential militant.

But British law-enforcement sources insisted to The Guardian that Italy never told them about Zaghba. “He was not a police or MI5 subject of interest,” the Metropolitan Police said.

Zaghba was shot dead along with his two accomplices, Khuram Butt, 27, and Rachid Radouane, 30, after they killed seven people in a knife-and-van attack in London.

Zaghba lived with his parents in Morocco until they split up and his Italian mother, Valeria Collina, 68, moved back to Italy.

Zaghba, who was born in Fez, resided in Morocco until he was 20. He was visiting his mom when he was arrested at the Bologna airport.

After his airport arrest, his mom told investigators she didn’t “recognize” her son anymore, The Guardian reported.

“He frightens me,” Collina told them. “He spends all day in front of the computer watching incredibly strange things.”

Collina told L’Espresso that her son phoned her from England Thursday, adding that in hindsight, it was a “call of farewell.”

“Even though he did not say anything in particular, I felt it from his voice,” she said.

As for her son’s radicalization, she said, “We have always tried to control his friendships, but the Internet came around. Then in London he was with the wrong people. I understand why the imams don’t want to celebrate his funeral.”

During the call, Zaghba and his mom discussed her upcoming visit to London — but then he dropped out of sight, and Collina reported his disappearance to local authorities.

She had no idea her son was involved in the London attack until Italian police showed up at her door on Tuesday to tell her Zaghba was dead.

Details about the other two attackers continued to emerge, including that Butt got into a “violent scuffle” last year with a member of an anti-extremism organization.

The Quilliam Foundation said Butt accused one of its members, Dr. Usama Hasan, of being an apostate who took “government money to spy on Muslims” and lunged at him twice when they got into a fight.

The group reported Butt to authorities, who said he was “already known to intelligence.”

Redouane was the only attacker entirely unknown to authorities — but friends of his estranged Irish wife, Charisse O’Leary, described him as an abuser who tried to force his spouse to live as a traditional Muslim woman.

After their 2012 marriage, Redouane spent 17 months in Morocco — and when he returned to Dublin, his views had become “extreme.”

Britain’s security services face new questions over news that perpetrators in the Manchester and London Bridge attacks were “known wolves” — extremists who’d attracted public attention, even proclaiming themselves would-be jihadis.

Yet authorities considered none to be anything more than a “suspicious person” — and certainly not an imminent threat.

One London attacker, Khuram Shazad Butt, actually appeared last year in a TV documentary on “The Jihadis Next Door” unfurling an ISIS flag in a public park.

He also had close ties to one of the 7/7 transit terrorists as well as to a radical preacher known as a recruiter of British Muslims to extremism.

And local Muslims had actually reported his frightening views to officials.

Youssef Zaghba, meanwhile, was detained last year in Italy while trying to travel to Syria to fight for ISIS. He told a security guard he was “going to be a terrorist.”

He wasn’t charged due to “insufficient evidence.” Italy insists it flagged him to UK authorities; London says it never got the word.

The late Prime Minister Margaret Thatcher often noted that security forces need 100 percent success, while terrorists “only need to be lucky once.” But even Foreign Secretary Boris Johnson now asks, “How on earth could we have let this guy or possibly more through the net — what happened?”

Voters will consider that as they go to the polls Thursday.

Police say they’ve thwarted 18 jihadist attacks since 2013 — five in the past three months alone. But the sheer volume of the threat, and the number of potential jihadis, is clearly overwhelming.

Current resources may well be insufficient to remain fully vigilant. That will mean some uncomfortable choices. Is Britain — or America — prepared to make them?