One person whose privacy was not invaded by U.S. intelligence was Tamerlan Tsarnaev, as he repeatedly visited the al Qaeda online magazine Inspire for its recipe “Build a Bomb in the Kitchen of Your Mom.”

Even after Russian intelligence asked the FBI to investigate Tsarnaev, the huge databases our intelligence services maintain in the name of our national security failed to alert the agents to Tsarnaev’s interest in building the pressure cooker bombs he would use to devastating effect at the Boston Marathon.

In the immediate aftermath of the Boston bombings, investigators did not fail to note similarities between those devices and the one described in Inspire. But the first solid intelligence specifically linking Tamerlan Tsarnaev and the magazine’s recipe came not from Big Brother but from his little bother, Dzhokhar, when he was interviewed by agents after allegedly helping to carry out the attack.

The problem is not just what the National Security Agency is gathering at the risk of our privacy but what it is apparently unable to monitor at the risk of our safety.

This lapse seems to include those who visit Inspire. They should have become a priority back in 2010, when it became known that Faisal Shahzad, the would-be Times Square car bomber, had used the pressure cooker recipe for his device. Shahzad also happened to use the same New Hampshire fireworks store as Tsarnaev to obtain crucial bomb materials, but he added other items for more punch. Had Shahzad’s device not fizzled, he almost certainly would have killed many more than did the Boston bombers.

After Shahzad’s online visits to Inspire became known, the magazine was called “the Vanity Fair of terror,” and experts warned that “open source jihad” perpetrated by “lone wolves” constituted the primary terrorist threat of the future. Maybe our intelligence community should commune with the kind of cyber marketers who seek to find out who is reading what in the real Vanity Fair with the aim of mining their personal data and zeroing in on them accordingly.

In the case of Tsarnaev, the databases also failed to uncover the online communications that Tsarnaev had with a known Muslim extremist in Dagestan. These online contacts were apparently the prime reason the Russians took an interest in Tsarnaev. The Russians developed their information by questioning the extremist, who reportedly listed Tsarnaev among his cyber pals.

If our agents had been able to make the link with the extremist, they might have done more than just have a chat with him and move on to the next possible jihadi. They would not have needed a multibillion-dollar intelligence apparatus to go on YouTube and see that Tsarnaev had posted a video playlist he labeled “Terrorists.”

As it was, Tsarnaev was able to build his bombs with nobody the wiser while he played Mr. Mom, watching his daughter as his wife was out earning the family’s sole paycheck. Many people have wondered aloud how the wife could not have known. The same question could be asked of a government that vacuums up billions of phone and Internet records.

As the NSA conducted surveillance on a global scale that seemed to confirm we are in an age where there is little or no privacy, Tsarnaev did just fine and was left to his own murderous devices. The latest issue of Inspire, which features a Photoshopped image of Tsarnaev in paradise with his smartphone and sunglasses, gloats that the author of the “Blessed Boston Bombing” had “managed to keep himself and his brother Dzhokhar away from the enemy’s attention until they rocked the marathon.”

“Inspired by Inspire,” the latest issue of the al Qaeda magazine says of the Tsarnaevs.

After the leaks about the scope of the NSA’s phone and Internet data mining, some supporters of the effort suggested that the Big Vacuum, whose cyber component is codenamed PRISM, had been instrumental in thwarting a September 2009 plot to bomb the New York City subways.

More likely, the break in that case came when British police busted a ring of alleged terrorists in April 2009. A search of a computer belonging to one of the suspects produced an email address that was linked to an al Qaeda operative. A court order was obtained for surveillance of that particular address, and investigators took note of a message that they traced to a man in Colorado named Mohammed Wali Zazi. The message contained a line that jumped out, given that “wedding” is an al Qaeda code word for an attack dating back to 9/11.

“The marriage is ready.”

The agents used traditional, entirely legal, and specifically targeted methods to place the dimwitted Zazi under surveillance. He was arrested before he and his fellow conspirators were able to put on a subway wedding with explosives considerably more powerful that those used in Boston, though still simple enough to be made in the kitchen of your mom.

Tsarnaev does not seem to have sent any coded messages to al Qaeda, as a lone wolf inspired by Inspire who arranged his own matrimony with murder. He likely only would have been caught if PRISM had done what it is supposed to be doing to justify its mega-infringements into our private lives.

The U.S. did a little schoolkid hacking of the al Qaeda magazine after the Boston bombing, garbling one page and rendering 20 others blank. But the site was soon restored with its image of the murderer in paradise.

There is a chance the hacking was a cover for some undetectable meddling, such as some way to track who visits the site and track them down the way modern marketers are able to track us down and slip in an ad for some new product when we go online.

Maybe if PRISM had stopped Tsarnaev before he bombed the marathon, that dizzy kid Edward Snowden would not have felt compelled to go from an overpaid analyst with a dancer girlfriend to a leaker seemingly bound for a long date with a prison cell in solitary.

Let’s just hope that the leaks do not prevent us from preventing some other attack, which is sure to come no matter how badly we want this longest of our wars to end.