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"I was going 24 hours a day, even in my sleep, trying to figure it out," he said. "I was totally obsessed. My daughter woke me up one night and told me I was having a dream about it."

But Keith is no homicide cop. He's an aerospace contract worker from Albuquerque �?one of hundreds of amateur cybersleuths who publish Web logs and post to Web sites and message boards devoted to the BTK case.

Some, like printer Terry Eckert of Austin, Texas, had a personal connection to the case. He was a childhood friend of Joseph Otero II, one of four family members killed by BTK in 1974.

But most, like Keith, came for the intellectual challenge and the chance to share their views with other amateur investigators.

And when Dennis L. Rader was arrested Friday and eventually charged with killing 10 people in and around Wichita from 1974 to 1991, it only fueled Internet interest in the case. Posters and bloggers speculated about motives, swapped rumors about clues that might have cracked the case and combed through old messages to see if BTK �?whoever the killer turns out to be �?had been reading and posting right along with them.

"There was someone who signed in as 'Dogcatcher,'" said Angela Avey, one of the site administrators for the California-based Web site catchbtk.com. "That's kind of an odd thing to sign in as. Now we're kicking ourselves for not finding out more."

Rader, 59, was a code enforcement supervisor in the Wichita suburb of Park City. One of his duties was animal control.

Messages purported to be from BTK could not immediately be verified �?but it appears he may have read at least one online account of his work. Police have said that one of his letters, sent last year, includes a "biography" whose chapter titles mirror those found on Court TV's crimelibrary.com site.

Law enforcement agencies also monitored the sites �?as Austin Ladwig found out in June 2004, when he came home in Sioux City, S.D., to find a detective's business card stuck in his front door.

The message: Get in touch. Now.

Ladwig, a bank card company worker, had posted his thoughts on the BTK case on The Wichita Eagle's message board. Police were interested in one particular post, giving directions from Wichita City Hall to the pay phone where BTK called authorities after a 1977 killing.

Just one problem, though: Ladwig is 27 �?four years younger than the oldest BTK case �?and has never been to Wichita.

"In three months, I went from knowing nothing about the case to being a person of interest," he said with a laugh.

When BTK first started killing, the Internet was in its embryonic stages. But when the killer resurfaced early last year, after a gap of more than two decades in his messages to Wichita media outlets, he found an army of amateur sleuths happy to dissect every possible clue from every conceivable angle.

"I don't think he took that into account," Geralyn Vertz, a stay-at-home mother from Sterling Heights, Mich., wrote in an e-mail to The Associated Press. "There are/were so many people disseminating every shred of evidence available ... following every little lead ... dissecting his every communique."

"Amateurs who care about things can now put their ideas into play or challenge the experts," said Lee Rainie, director of the Washington-based Pew Internet and American Life Project. "That's one of the biggest things the Internet has done."

Some of the theories were far-fetched: BTK was a woman. BTK was three people. BTK was dead, and someone else had found his trophies and picked up the game.

But some conjectures turned out to be too close for comfort.

Steve Huff, an operatic tenor from Atlanta who maintains a BTK page on his Web log, or blog, speculated in December that the killer would be a balding, stocky, mustachioed neat freak who wore glasses with heavy frames.

Rader is balding, stocky, has a mustache and wears glasses. Another code enforcement officer described him to the Eagle as a meticulous dresser who kept every pen in his day planner in perfect alignment.

"Initially, I felt vindicated," Huff said. "I thought, 'I scored on a couple of things.' Then I felt chilled by it."

Eventually, the case will wind down �?and while BTK enthusiasts might miss the thrill of the chase, they said they're glad to see a suspect in custody.

"If you had to say, 'Would I rather be entertained at my computer and him still be on the loose, or have him be captured and find some other kind of other entertainment?' most people would rather find something else to do," said Amelia Hardy, a senior at Georgia State University in Atlanta.