How could so many have missed what is now so obvious?

Nor, apparently, did the state licensing agency that reviewed Robert Crimo’s application to purchase guns. Crimo managed to evade the state’s red-flag law, intended to keep guns out of the hands of people with violent tendencies, despite two instances that in retrospect should have served as warnings.

Crimo attempted suicide in April 2019. Then, in September of the same year, he announced to his family that he wanted “to kill everyone.” Police visited the Highland Park home where Crimo lived with his father and uncle, and confiscated 16 knives, a dagger and a sword.

Because no complaints were filed, there was no further investigation.

Still, if these incidents didn’t raise red flags, then the world must be color blind. Three months later, Robert Crimo began buying guns with his father’s signed approval. The real quiet kid passed four federal background checks, purchasing five guns — including the one used at the parade.

So, let’s say you’re Robert Crimo’s father, who owns a popular Highland Park deli, and your kid wants a gun. You know that he has attempted suicide. You know that he’s made threats of killing people. Then, you help him get his hands on guns?

The question then becomes whether Bob Crimo bears some responsibility for his son’s actions. Plenty of commentators, criminal justice experts and psychologists have sounded off through the years about whether to allocate blame beyond the perpetrator. Some cities, such as Philadelphia, already punish parents when their kids don’t adhere to warnings and rules.

Is this fair? Every parent knows that raising kids is a crapshoot. Sometimes the most attentive parents, through no fault of their own, produce some of the worst human beings. And some of the worst parents don’t deserve their children, who somehow, miraculously, transcend their unfortunate circumstances to become gold-standard young adults.

Bob Crimo says he accepts no responsibility for what his son allegedly did. When asked why he allowed his son to buy guns, he said he assumed the guns would be used only for target practice. Knowing what we now know, this seems naive if not obtuse. Judging the father also seems unduly cruel just now.

How discerning of an adult child must a parent be? Answer: As discerning as humanly possible. In this age, of internet access and deepfakes and endless violent games — and widespread weapons — an assume-the-best attitude by a parent is a recipe for potential life-changing catastrophe. Trust, but verify, as President Ronald Reagan used to say.

Had Bob Crimo been nosier, he might have discovered that his quiet son was quite loquacious as his online persona named Awake The Rapper. Posting thousands of videos, songs, messages and photos, he was a young man clearly obsessed with violence. In one video, Robert Crimo is wearing a helmet and vest inside an empty classroom where he scatters bullets across the floor. He was also a dedicated contributor to an online forum where people share violent photos and videos of people dying.

How could so many have missed what is now so obvious? If my kid came home with facial tattoos, I’d figure something was up.

The breakdown of the state’s red-flag strategy reminds us that no barrier to violence is foolproof against criminal intent. I learned this from an expert years ago when interviewing a convicted murderer in the Florida State Prison about his thoughts on gun control. He loved the idea, he said, “because people like you will be disarmed, and people like me will always have a gun.”

That point came home Friday with the assassination of former Japanese prime minister Shinzo Abe. Japan’s gun laws are so strict that private gun ownership is rare, and shootings rarer. The suspect, who, according to law enforcement, has confessed, used a crude, homemade gun. While he was able to kill one man, he wasn’t able to kill more, as American mass murderers routinely do with assault-style weapons.

Given human willfulness, the fallibility of red-flag laws and the logistical impossibility of monitoring everyone with a pattern of violence, it seems that certain guns are the problem. As for parents, though sometimes clueless, they’re only human. Which, until Judgment Day — or when animals reclaim the kingdom — isn’t a crime.