When 25-year-old Kimveer Gill went on his recent shooting rampage at Montreal's Dawson College, killing one student, injuring 19 others, then committing suicide, reporters seeking to explain his homicidal snap mined a treasure trove on Gill's personal blog. "You will come to know him as the Angel of Death," he wrote of himself on VampireFreaks.com. "He is not a people person." His Web journal featured a photo of his hoped-for headstone, including his name and the epitaph: "Lived fast, died young. Left a mangled corpse." Gill wrote, prophetically, that he wanted to die "like Romeo and Juliet — or in a hail of gunfire."

When 21-year-old Melinda Duckett, a Florida mother of a missing 2-year-old, shot herself earlier this month, she left behind an elaborate personal journal at MySpace.com, a massive Web networking site. "I have had to fight to keep my son, whom I am extremely proud of," she wrote in one post. "Why cannot anyone understand/ the burdens I hold within my hand/ Life can not be all fun for I/ so many issues that I have to hide," she posted in June.

And when 19-year-old Alvaro Castillo killed his father before a shooting spree at Orange High School in Hillsborough, N.C., several weeks ago, Castillo's MySpace page was found to list "handguns, shotguns and rifles" among his "general interests." Among his "pics" is one of himself brandishing a pair of scissors as he appears ready to stab an unidentified young male in the head. "Attempted Murder," the caption reads. "Are you scared? Ha ha." On his list of people to meet: John Hinckley Jr., Michael Moore and God.

Increasingly, ours is a world in which no emotion is real unless it's expressed on a reality show, and no murder is a murder unless it's blogged in advance. And there are all sorts of legal implications to this explosion of virtual fingerprints — not only with respect to solving crimes, but in terms of inspiring others.

Consider, the copycats. Gill and Castillo apparently were preoccupied with the 1999 killings at Columbine High School. Gill loved to play "Super Columbine Massacre," a computer game that simulates the shootings. And on Aug. 29, just before he took a sawed-off shotgun to his old high school, Castillo sent a videotape and letter to the Chapel Hill News claiming to be obsessed with Columbine.

There is nothing like the World Wide Web for forging deep and meaningful bonds between antisocial outcasts. Before the advent of the Internet, Gill might well have lived out his days hating others in his parents' basement, but VampireFreaks.com afforded him the opportunity to reach out to thousands of other petulant misanthropes. "Can I go play with you?? I wanna go hunt down the preppies with you!!" a 19-year-old Indianan calling herself caranya wrote to Gill the day before the killings.

Lest you think the overwhelming reaction is one of outrage, it's worth pointing out that after the Montreal shooting spree, traffic on VampireFreaks.com exploded. Networking sites such as MySpace and Facebook also make things vastly easier for would-be criminals. US News & World Report recently revealed how easy it is for predators to locate identifying information about vulnerable kids.

But the Web also dehumanizes and distances. That might explain how Heather Kane, a 22-year-old Arizona woman arrested last week in connection with a conspiracy to attempt murder, was allegedly able to pay $400 to an undercover police officer posing as a contract killer. The money was supposedly to bump off a woman she believed her ex-boyfriend was dating; Kane discovered the rival on his MySpace page, from which she downloaded the intended victim's picture, home address and workplace information — one-stop shopping. Police later observed that she showed no emotion as she commissioned the hit.

Why would she? Her alleged victim was probably no more real to Kane than the virtual students Gill mowed down playing "Super Columbine Massacre."

These MySpace postings are also reshaping criminal prosecutions. A star witness in another Canadian murder trial associated with www.VampireFreaks.com discussed the case on her blog, resulting in a mistrial. A California prosecutor has abandoned his efforts to shut down the MySpace page of a defendant who allegedly used her car to run over and kill her former boyfriend's new girlfriend. The defendant's mother posts trial documents on the page that could taint the jury pool.

It's not at all clear that increasing the regulation or monitoring of these networking sites is the answer. Beyond the many obvious privacy issues and the fact that it's impossible to differentiate true threats from fantasy on the Web, police departments don't have the resources to monitor a Web site such as MySpace, which signs up 230,000 new members a day. Moreover, some of the most disturbed users seem to relish their belief that they are subject to constant police surveillance: "I know you're watching me," Gill wrote last February. Police in fact knew nothing of his Web page at the time.

As a legal matter, we treat the Internet as though nothing on it is real. We aren't yet sure how to regulate it, and most of us still use it with little regard for the legal consequences of what we post. That makes it a perfect medium for people hoping desperately not to be invisible. Castillo and Gill are described by former school friends as unmemorable. Yet each was the hero of his Web page.

In the end, these pages aren't real, although the victims and alleged victims of their owners are quite dead. And even their authors' efforts to use the Web to leave a permanent mark have been thwarted. If you look for Gill's page on VampireFreaks .com, you'll find it has been removed, replaced by the apt message: "This User Does Not Exist."

Dahlia Lithwick covers legal affairs for Slate, the online magazine. She wrote this commentary for The Washington Post.