(CNN) -- Committing such heinous crimes as sex abuse and murder are unthinkable enough to most of us. But it's almost equally mind-boggling that the perpetrators would then confess, or even brag about, such acts on the Internet.
Even so, in cases as mundane as vandalism or as horrifying as gang rape, accused criminals are exemplifying a growing truth of the social-media age: To some, nothing is too sacred, private or damning to share online.
"Social media exposes the crimes, along with the poster's need to feel important or powerful," said Pamela Rutledge, director of the Media Psychology Research Center at the Massachusetts School of Professional Psychology. "However, in most cases, it appears that the need for bravado is much greater than any concerns about getting caught."
The latest high-profile instance happened Thursday, when a Florida man allegedly killed his wife and posted a photograph of her body, along with a confession, on his Facebook page.
"Im going to prison or death sentence for killing my wife," wrote Derek Medina, 31, of South Miami. "(L)ove you guys miss you guys takecare Facebook people you will see me in the news."
The gruesome image was shared thousands of times before Facebook was alerted and deleted it several hours later.
It shocked his own Friends list. Among the responses: "WHAT??????" "What happened???? derek."
But social-media posts about crimes are surprisingly common. Just a few of the most widely publicized in recent times:
-- An investigation into the rape of an unconscious 16-year-old girl by high school football players in Steubenville, Ohio, began after some of the accused posted pictures and video of the girl on Facebook, Twitter and Instagram.
-- The alleged 2011 rape of Rehtaeh Parsons, then 15, in Novia Scotia by four teens was discovered after the teens reportedly shared a photo of her online and via text messages. Two of them, now adults, were charged with child pornography this week. Parsons, at age 17, hanged herself and, in April, was taken off life support.
-- In 2011, a Pennsylvania teen pleaded guilty to raping an intoxicated 15-year-old girl, then turned to Facebook, looking for a hit man to kill her. " "I got 500 on a girls head who wants that bread?" he wrote. "Hit me up anyway possible." The man who responded was, in fact, an undercover detective.
-- A Hawaii man was charged after posting a video titled "Let's Go Driving & Drinking!" in which he appears to open and drink a beer while driving and talking to a camera for more than five minutes.
Michele Nealon-Woods, national president of the Chicago School of Professional Psychology, notes that criminals were publicly confessing or boasting of their crimes long before anyone heard of Mark Zuckerberg and tweeting was something done by birds, not humans.
In 1888, the notorious "Jack the Ripper" is believed to have sent at least three letters to London police, taunting them and telling them when he planned to kill again.
In northern California, the so-called Zodiac Killer did much the same nearly a century later. He sent dozens of letters to police and the media in the late 1960s and early '70s -- some of them cryptic puzzles that have never been solved.
Throw in timeless tales of jailhouse confessions and barroom braggarts and it's clear that the base instinct here is nothing new.
"The new part of it now, though, is that when people did very dangerous, aggressive bad things to other people in the past, they didn't have the medium with which they could share the information," Nealon-Woods said. "There is that aspect associated with aggressive crime that we've always seen.
"What social media has done is give people with those propensities a whole new platform."
But Nealon-Woods thinks there's more to it. Social media, she says, is a tiny blip in the long and evolving history of human communication. And no on one can be really sure what, if any, impact it will ultimately have on the way we behave.
"It's one of those things that are evolving," she said. "It has been a major, really disruptive innovation in our lives and, like anything that us human beings do, it's taking us quite a while to adapt and change and respond."
While millions, if not billions, of people use social media in healthy, happy ways every day, Nealon-Woods said there are some -- and not just criminals -- who haven't adjusted so well.
Their inability to pick up the new social norms result in behaviors ranging from Internet trolling to oversharing to the sort of misguided posts that can embarrass users or land them in jail.
The physically isolating aspect of social media is probably part of the equation, she said. When we can communicate with other people without seeing or hearing them, something in the brain makes it harder to remember that there are still consequences for what we say, she said.
"We've removed that human interaction, and that is giving people a false sense of the extremes they can go to," Nealon-Woods added. "I really do believe that's one of the main reasons that people are posting things where other people are saying, 'Oh my gosh!' "
Social media is a young form of communication that will take time for some people to adjust to, she said. In the meantime, Rutledge, the Massachusetts researcher, notes one upside of when awkward online behavior and crime mix.
"The good news is that compulsion to brag about getting away with these activities increases the probability of getting caught," she said. "Without social media, it would have been much harder to find the culprits, much less prosecute (them)."