Shortly after George Sodini killed himself following his shooting of 12 women in a fitness club, his diary describing his hatred of women and plans to someday carry out such a tragedy showed up online.

Within a day of the shooting, Web surfers could find benign YouTube videos and Mr. Sodini's musings about underage girls on online forums.

George Sodini

Finally, someone posted links on the Internet to Mr. Sodini's receipts from purchases he made online of ammunition and large-capacity magazines for his guns, as well as records of his Google search history -- including queries like "mass murderer profiles," "murder suicide statistics," and "going to die anyway."

The lightning speed and reach of the global communications network became clear when a hacker decided to see if he could break into the account of a killer and let the whole world follow on a trek through the world of a dead man.

The items, when viewed individually, could be harmless minutia. But when viewed as a whole, it foreshadows Tuesday's horror.

"I think the fascination comes from being able to see into the private mind of a mass murderer," said Alex, the Canadian computer hacker who compiled much of Mr. Sodini's online life into a public Web site for all to see.

When he learned that the man responsible for killing the three women at an American fitness center Tuesday was an information technology professional -- Mr. Sodini worked as a systems analyst at Pittsburgh law firm K&L Gates -- Alex saw it as a challenge to learn as much as he could about him by hacking Mr. Sodini's information.

Alex, who spoke on the condition that his last name not be used, said it was simple.

"This was fairly easy. I didn't even have to do anything to a server. I didn't force my way in."

Instead, using Mr. Sodini's Web domain, georgesodini.com, Alex was able to find his e-mail address. From there, he went to the webmail server that Mr. Sodini used, and clicked on the box that asked if he forgot his password.

That prompted a security question asking Mr. Sodini the name of his favorite pet. In his previous Google searches, Alex had already found the answer to that. He typed it in, and just like that, he accessed Mr. Sodini's e-mail, and from there other, older Web pages the man had kept, his Gmail account, and therefore his Google search history.

In addition to looking up terms about mass murder, Mr. Sodini did searches on "corruption of minors," and "age of consent Pennsylvania."

He queried things like "social phobia," "cognitive therapy," and "avoidant personality disorder," and other innocuous things, like lyrics by the singers Pink and Van Morrison.

Alex also found YouTube videos Mr. Sodini posted more than a year ago of him talking about his feelings and another of him giving a walking tour through his Scott home.

While the videos had only a couple dozen hits when Alex found them, by the end of the day yesterday, they numbered more than 25,000.

"It's just curiosity," Alex said of hacking Mr. Sodini. "It has been interesting to try and reconstruct what is left of his online life."

Louis B. Schlesinger, a professor of forensic psychology at John Jay College of Criminal Justice in New York, said people have always been fascinated by crime.

It is particularly so, he said, if the crime is something different or extraordinary.

"It's very discomfiting when there's mass murder," Dr. Schlesinger said.

And so people will try to gather as much information about a person as possible to reassure themselves that there was something tangibly wrong with the killer -- a diagnosable mental illness, past abuse, or even a brain tumor -- to show that the person was unlike everyone else.

"Going off and losing control is very frightening," the professor said.

But there are other reasons to be intrigued by crime.

"Many people get some sort of vicarious gratification with criminals who are very clever," Dr. Schlesinger said. "In a case like this, a lot of people, strangely enough, can identify with him."

Alex agrees.

"I've found, and I'm sure other people have found, similarities in their lives with his -- at some point feeling lonely or removed from other people.

"He looked normal, had a normal job, led from outside perspectives a normal life. But in reality he was not well, and he snapped."

Though his Google history shows Mr. Sodini clearly wanted to learn more about a variety of mental illnesses, it is unknown if he ever sought treatment of any kind.

"In retrospect, things are so clear," Dr. Schlesinger said. "Could this have been prevented? Impossible to know."