As 8-year-old Martin Richard was laid to rest on Tuesday, the FBI seemed only right to insist it could not be fairly blamed for failing to prevent his death and the death of two other innocents who perished in the Boston Marathon bombing.

The FBI did not ignore the vague inquiry from the Russian government about Tamerlan Tsarnaev. Agents duly interviewed him and ran his particulars through the available databases. They seem to have been correct in determining that he did not have any connections with organized terror groups.

But the very fact that the FBI had interviewed Tamerlan back in 2011 presents the possibility, however slight, that the death of another person who was buried Tuesday really might have been prevented.

That other funeral was for MIT Police Officer Sean Collier, and the question is, why the investigators who interviewed Tamerlan did not recognize him before the photos of the bombers were made public.

Agents and cops may forget a name, but they seldom forget a face. And had an investigator exclaimed, “Hey, I know that guy!” the FBI and the Boston cops could have been outside the Tsarnaev home in 15 minutes. Tamerlan and his younger brother, Dzhokhar, might have been grabbed before the public release of their pictures, before they turned so desperate that they walked up to the cruiser where Collier sat and allegedly executed him.

A retired FBI counterterrorism supervisor says he cannot imagine that the Boston office failed to show everybody the photos prior to sharing them with the world. Maybe both the investigators who questioned him had retired or were transferred. Or perhaps the bosses were so worried about leaks that they did not include everybody in the loop.

Whatever the explanation, the investigators who interviewed Tamerlan no doubt are feeling as if they have landed in their worst nightmare. The situation brings to mind the famously hard-luck FBI agent James Hosty, who ran another routine investigation related to Russia, that of Lee Harvey Oswald just prior to the Kennedy assassination. Hosty had found no evidence that Oswald was a threat to national security, despite having lived in the Soviet Union and having a Russian wife.

“I can see some poor guy telling himself, ‘I’m the new Jim Hosty,” the retired supervisor said of those who seem to have been similarly blameless in finding Tamerlan to be no apparent threat.

Any new Hosty can reassure himself at least that the Tsarnaev brothers apparently did not begin to secure the main ingredients for their bombs until February of this year. That was when they took advantage of a two-for-one sale at Phantom Fireworks in Seabrook, N.H., paying just $200 for two “Lock and Load Kits,” from the Barely Legal brand, advertised as each containing “24 power-packed, MAXIMUM LOAD Canister Shells.”

Phantom Fireworks suggests that the kits do not contain enough gunpowder to make a bomb, but the “How to Build a Bomb in the Kitchen of Your Mom” recipe in the al Qaeda magazine Inspire that the Tsarnaev brothers apparently followed says “the powder from fireworks” or even just the scrapings from matches is all that is needed for a pressure-cooker device. The destructive force is generated by combustion in the container strong enough to confine the resulting gases until there is an explosion.

The brothers further followed the recipe’s recommendation to glue shrapnel on the inside of the cooker. They used ball bearings in keeping with Inspire’s advice that “the best shrapnel are the spherical shaped ones.” They also observed the final step.

“Place device in a crowded area,” the recipe says.

All that came from an online publication. As it says in Inspire, “we are delivering you our military training right into your kitchen.” The brothers were able to turn themselves into deadly terrorists without needing to connect directly with al Qaeda or any other terror outfit in a way the FBI could have been expected to detect.

In an ideal world, the agents would have gone back to check on Tamerlan and noted that he had posted a YouTube playlist he dubbed “Terrorists.” But they had many other tips to follow where the databases did turn up something worth pursuing.

Still, at the very least, the agents should have recognized Tamerlan. That is, unless they for some reason did not have a chance to see the photos before the rest of us did and before the brothers went on their rampage.

By one account, Tamerlan told the driver of the car they carjacked after allegedly killing Collier: “We just killed a cop. We blew up the marathon. And now we’re going to New York. Don’t fuck with us.”

Well, Collier’s fellow officers did not hesitate to fuck with them and in so doing faced a final pressure-cooker bomb that might otherwise have added to terrorism’s toll in New York. One of Collier’s police academy classmates was severely wounded during the shootout and there was almost another police funeral.

Thankfully, MBTA Transit Police Officer Richard Donohue is expected to survive. We are indebted to him and to all those in law enforcement who assisted in bringing the Tsarnaev brothers to justice.

And yes, that includes the FBI.