I remember the first person I arrested for murder.  I had been out of the LAPD academy only a month or two, and my training officer and I were assigned a radio call known as a “welfare check.” These calls most often arise when someone is unable to contact an elderly relative or friend.  We went to the house in question, the home of an elderly widow, and found no evidence of a forced entry or any other outward sign of trouble.  But given the woman’s age and the accumulation of mail and newspapers at her front door, and as none of her neighbors had seen her in some time, my partner made the decision that we should break in.  We did so, expecting to find the woman dead of a heart attack, a stroke, or any of the other natural causes that claim people her age.

Yes, she was dead all right, but there was nothing natural about what had killed her.

When the homicide detectives arrived and assessed the scene, they told us it appeared that the woman had been raped and then stabbed to death with a kitchen knife.  The killer, having worked up an appetite, cooked and ate a meal as the woman lay dying in the next room.  To this day I am haunted by the thought of the terror she must have felt in those final moments of her life.  Who could have done such a thing, I wondered.

Later, with the detectives still sifting the crime scene for evidence, there was little for my partner and me to do but stand near the yellow crime-scene tape and keep the curious at bay.  A young man of about 20 approached and asked us what was going on, and in the most perfunctory of terms we told him that the woman in the house had died.  A detective in the house contacted us by radio and told us to step out of earshot from the man, and when we had done so the detective informed us we had been talking with the likely killer.

As an eager rookie, my inclination was to slap the handcuffs on him as quickly as I could.  My partner, with his greater experience and accompanying wisdom, played it differently.  He continued to engage the man in small talk, cleverly eliciting some admissions that would later prove valuable in the murder case against him.  We would come to learn that the woman had befriended the killer — a neighbor — some years before and often hired him to perform odd jobs around the house.  He had completed one such job before raping and killing her.

While the man struck me as a bit odd, to my then-untutored eye there was nothing in his demeanor that suggested he was capable of the horrible crime he had just committed.  In speaking with other neighbors later, I didn’t find one who wasn’t completely shocked by what the man had done.

Which brings us to the unfathomable, decade-long ordeal of Amanda Berry, Gina DeJesus, and Michelle Knight, the three women recently freed from their kidnapper in Cleveland.  How, we wonder, could one man kidnap and hold in captivity even one person for so long without being discovered?  How twisted must a man be to carry out such a crime not just once but three times?  And how can so twisted a person move among us without our detecting the depth of his malevolence?

We want to comfort ourselves with the delusion that we can spot the dangerous people in our midst.  We look at the man accused in the Cleveland case, Ariel Castro, and we tell ourselves we would have known something was amiss behind the walls of his ordinary looking clapboard home.  Never in my neighborhood, we say.

But the truth is that most of us haven’t a clue about what goes on inside our neighbors’ homes, even in those neighborhoods described, like Ariel Castro’s, as “tight-knit.”  As anyone who reads the papers knows, this term is most often a press euphemism for “poor” or “crime-plagued,” and indeed the Cleveland Police Department’s crime map reveals that officers in Castro’s neighborhood are kept busy.  Zoom in on the map to the area just south and west of the I-90/I-71 interchange, expand the date range from the last seven days to the last 30, 60 and 90, and watch the dots on the map multiply like so many poisonous spores in a Petri dish.

I’ve spent most of my police career in Los Angeles working in similar neighborhoods, and even in those that genuinely are “tight-knit” there are always those few individuals who, like Ariel Castro, are themselves at varying stages of coming unraveled.  I’ve arrested murderers who had been living right under the noses of people who couldn’t bring themselves to believe that their friend, neighbor, or even family member had shot, stabbed, or bludgeoned someone to death.  Once he washes the blood off his hands, your typical murderer looks much the same as anyone else.

Did the police make mistakes in their handling of the three women’s disappearances?   Perhaps.  Michelle Knight’s name was dropped from an FBI database of missing persons only 15 months after her disappearance, but there is little cause to believe her continued presence in the database would have led to her recovery.  After all, Amada Berry’s and Gina DeJesus’s names were in the same database the entire time they were held, to no effect at all.  And as for those who say the police should have done more to find the women, one must ask: What more could they have done?  In all three abductions the police had no witnesses to describe a suspect and no crime scene from which to pluck forensic evidence.  And there was nothing about Ariel Castro that would have offered police cause to suspect him in the cases or to search his home.

No, it isn’t easy to spot the evil person next door.  Witness the various characterizations of the Tsarnaev brothers, the Boston Marathon bombers, whom most acquaintances described as ordinary young men incapable of such a horrific crime.  And now we know that the brothers have been implicated in a 2011 triple murder in Waltham, Mass., not far from the Watertown neighborhood where the elder brother was killed in a shootout with police and the younger one was captured.  How many of their friends suspected they were such cold-hearted killers?  How many of the strangers they encountered every day saw even a hint of the darkness in their souls?  None of them, I’m sure.

So it is with Ariel Castro.  Yes, now that he’s been identified as the proprietor of the Seymour Avenue Dungeon, his neighbors are making claims that they suspected him of bad things all along.  There was a naked woman chained up in the backyard, went one report, but the police failed to investigate.  All of these tales were concocted after the rescue, police say; there was nothing about Ariel Castro or his house that would have offered the slightest hint at what he was doing behind his closed door.

Ariel Castro is accused of unspeakably evil acts, but like the Tsarnaev brothers, like that murderer I arrested years ago, like all those killers on the loose in Chicago and most other cities you could name, he went unrecognized until the evidence of his crimes leapt out and grabbed someone’s attention.

Not every criminal — or even every murderer — sinks to the level of depravity occupied by the likes of the Tsarnaev brothers and Ariel Castro.  But consider: The Boston Globe reported that police solved 43 percent of the city’s murders in 2012, leaving 57 percent of the killers out and about and free to kill again.  In Ariel Castro’s Cleveland the police do a better job of things, with a 2012 murder clearance rate of 69 percent, but that still leaves 31 percent of its killers on the loose.  And in Chicago, a mere 132 of the city’s 507 murders that occurred in 2012 were solved, for a clearance rate of just 26 percent.  That’s a lot of killers running around out there going to restaurants and the movies and partaking in all the other pleasures the less homicidally inclined enjoy, maybe even sitting in the theater right next to . . . you.

Enjoy the show.