While Mayor de Blasio occupied himself Wed­nesday with frivolous tweets about bagels, a family is grieving for a grandmother whose murder immigration officials are blaming on the mayor’s “sanctuary city” policy.

New Yorkers don’t care whether the mayor likes his bagels toasted or with extra cream cheese. We care that our city feels more dangerous by the day.

We care that 92-year-old Maria Fuertes was sexually assaulted, choked and left for dead outside her Queens home one freezing night last week.

We care that the 21-year-old ­illegal immigrant charged with her murder would not have been on the street if the city had complied with a simple detainer request from US Immigration and Customs Enforcement officials, pending possible deportation.

Instead, like every one of the 2,916 detainers the NYPD received from ICE in the 12 months to June 30 last year, the request to detain Guyanese national Reeaz Khan was ignored, with fatal consequences.

What a horror were Fuertes’ last hours on Earth. Born in the Dominican Republic, the mother of two was, by all accounts, a gentle, much-loved figure in her neighborhood.

She had gone out to search for returnable empty bottles to supplement her income when she was attacked from behind by a stranger just after midnight on Jan. 6, surveillance video shows.

A post-mortem found horrific injuries including a broken spine, fractured ribs, bruising on her chest and neck, internal hemorrhaging and injuries to her vagina. She was found on the ground two hours after the ­attack and died later at Jamaica Hospital Medical Center.

No one deserves such a horrible death.

New York’s 5-year-old sanctuary-city policy means that, instead of dangerous criminal illegal immigrants being deported straight out of jail, the NYPD releases them onto our streets to disappear.

Now, of course, we have the double whammy of Albany’s criminal-justice “reforms” that mean the criminals probably won’t even go to jail in the first place.

De Blasio’s sanctuary policy puts the NYPD in an invidious position. Instead of ­cooperating with fellow law-enforcement officials at ICE, police are compelled effectively to ­obstruct them.

In Khan’s case, the two agencies are now embroiled in an unseemly public dispute over who’s to blame — while de Blasio sticks his fingers in his ears.

The NYPD claims it never ­received ICE’s request to detain Khan back in November after he was arrested for allegedly assaulting his father.

“At that time, the NYPD did not receive an ICE detainer in regard to this individual,” police spokeswoman Sgt. Jessica ­McRorie said.

But ICE responded by releasing a copy of the fax cover page from the original request showing it was transmitted to the NYPD at 7:41 a.m. on Nov. 27, hours after Khan was arrested.

“It is the height of hypocrisy for NYC to blame ICE for this tragic crime,” irate ICE acting federal director Matthew Albence said in a tweet.

“The mayor & police chief have continually celebrated that they don’t honor ICE detainers, & to deflect the criticism for this completely preventable murder is incredibly disingenuous & shameful.

“ICE could’ve wallpapered the precinct with detainers [and the NYPD] would still not have ­honored them.”

That’s the truth. Maybe the fax machine at Queens Central Booking was out of paper on Nov. 27, or maybe an overworked officer threw the ICE request in the garbage.

It makes no difference, because it never would have been honored. It’s a farcical dance that both sides know is futile.

“It was a deadly choice to release a man on an active ICE detainer back onto the streets after his first arrest included assault and weapon charges,” said Thomas Decker, field-office director for ICE’s enforcement and removal operations in New York.

“New York City’s sanctuary policies continue to threaten the safety of all residents of the five boroughs, as they repeatedly protect criminal aliens who show little regard for the laws of this nation.”

You can understand his frustration. Last September, ICE arrested 82 illegal immigrants in the New York region. The NYPD promptly released more than half, despite the fact they faced charges including rape and child pornography.

De Blasio regards his sanctuary-city law as a social-justice measure.

But where is the social justice in releasing rapists onto the street to prey on vulnerable women? Where is the social justice in choosing the rights of criminals over the rights of victims?

“We will not deport law-abiding New Yorkers,” the mayor said in 2017 while threatening to sue President Trump over a federal crackdown on undocumented immigrants. “We will not tear families apart.”

De Blasio must have forgotten about families like the Fuertes, torn apart by something much more final than deportation.

Dems’ ‘losing’ strategy

Gloomy Democrats and their media pals already are setting up alibis in preparation for losing the November election to President Trump.

Hillary Clinton prepared the ground last week, saying the fix is in for 2020. “Russians appear to be rerunning their 2016 hacking playbook, once again to benefit Donald Trump,” she tweeted.

Progressive New York writer Frank Rich expressed the fear that Trump will win, in part because of “a stacked Electoral College.”

In Tuesday’s Iowa debate, Joe Biden was apocalyptic about the prospect: “We can overcome four years of Donald Trump, but eight years of Donald Trump will be an absolute disaster and fundamentally change this nation.”

If his fears come true, get set for a turbocharged Resistance that will make the last three years look tame.

But if they had spent more energy trying to win the next election and less on making excuses for the last one, Dems might not be in such a parlous state.

Trudeau’s plane blame a shame

What kind of a rotten ally is Justin Trudeau to try to blame America for Iran’s downing of a Ukrainian passenger jet?

This is the Iranian line, despicably echoed by a prime minister who should be consoling the families of the 57 Canadian victims, not stoking irrational anger against Trump.

“I think,” said Trudeau, “. . . if there was no escalation recently in the region, those Canadians [on board] would be right now home with their families.” In other words, it’s President Trump’s fault for deciding to take out Iran’s top general, Qassem Soleimani.

The Canadian pipsqueak would do better to listen to former Obama National Security Adviser Gen. James Jones, who says it was “absolutely correct” to target Soleimani and it could be a “game-changer” in the region.