By ETHAN SACKS
mostNEWYORK Assistant Editor

ome people hold housewarmings when they get a new house. Tom Arriola staged a murder.

"Joan Woodley, the managing editor of the Oxford Eagle, was found shot to death in her office. Suspected is Chase McFadden, a staff reporter, who had an on-again, off-again romantic relationship with the victim."

The above passage comes from the official Web site of the Yoknapatawapha County police, www.crimescene.com. On the surface it seems like an honest attempt by local law enforcement to solve a real life murder. Upon closer inspection, however, the site is not only maintained by Arriola but the murder victim is just an actress lying in fake blood in his new Oxford, Mississippi home.

"Everything was realistic, except I didn't murder anybody," said Arriola.

While the rate of real crimes on the Internet has been growing by 4.7% a week, according to the Web Police, an international organization that tracks everything from simple e-mail abuse to terrorism, there has been another kind of crime running rampant on the Web. Dozens of murders, kidnappings and robberies have popped up on the Net that aren't quite as serious: Interactive mystery sites that allow users the opportunity to sift through everything from video files to java-script dialogue sequences to play detective.

The case of www.crimescene.com began with the murders of two Supreme Court justices and a mysterious legal brief. Or at least that's how fellow Mississippi native John Grisham's book, "The Pelican Brief" started.

That gave Arriola an idea. "I thought, 'Wouldn't it be great to read the actual brief?' To prove it was a good idea I invited some friends over and started the Web site. I spread blood all over my apartment and took pictures. I asked my friend Valerie Wilson if I could kill her and I asked her boyfriend Greg Giblin if he would be the murderer." In keeping with the literary theme, Arriola borrowed a page � or, at least the name for the fictional county � from another Mississippi native, William Faulkner.

Crimescene.com went live in January of 1995 and the collection of faux photos and police reports was so realistic that Prodigy asked its users to assist in solving a real-life crime. When it was discovered that the murder was fictional � there is no disclaimer on the site � there was an uproar that made national news broadcasts. The exposure, however, put Yoknapatawapha on the map. Since then, the cases have become more elaborate. Arriola even collaborated with a molecular biologist from MIT to make the DNA evidence more authentic.

"It started out with just me," said Arriola. "Now we have a scriptwriter in California, we have actors all over the country and a guy in Germany who does our computer animation."

"Homicide: Second Shift" on NBC's Web site is probably the most advanced of the interactive mysteries. Based on the network's gritty Friday night drama, the online version has its own plot lines of death and dismemberment in Baltimore. Utilizing actors (including the televised version's Yaphet Kotto in one case), well-developed scripts, sleek graphics and java navigation across the crime scenes � the site definitely boasts a sizable programming budget � it keeps the feel of the series and gives users a chance to share info in chatrooms afterwards.

Case.com, which also celebrated its two-year anniversary this month, takes the budding genre in a different direction. "The idea is that people needed a five minute lunch-break and we'd provide it with interactive mysteries," said Steve Schaffer, president of Newfront Communications, which produces Case.com. Three times a week, the site offers mysteries that can be cracked in three-to-five minutes; the site also e-mails free weekly mysteries to users on its mailing list.

"We used to have to approach the freelance writers and now they approach us," said Schaffer, "It's the most popular stop on the Internet for mystery fans."

Apparently, pretend cyber P.I.s has become popular enough to have created a whole "MysteryNet" network of spin-offs, including an online mystery bookstore and a retrospective on the history of the genre. According to Schaffer, the next spin-off, launching next month, is a "Case.com for Kids" site that offers Goosebumps-like thrills for children.

With the success of these sites, expect the interactive crime spree to continue.