Day by day, James Keith became more obsessed with the BTK serial killer. Just one more clue, he thought, and he could crack the case that had baffled authorities in Wichita since the 1970s.

“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, N.M. — 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 sleuths.

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 whether 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.

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.

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.

“Initially, I felt vindicated,” Huff said. “I thought, ‘I scored on a couple of things.’ Then I felt chilled by it.”