The cyber sleuth logs on and enters the seedy underworld of the Internet.

He's inside a chat room. Like the others, he's anonymous: just another meaningless screen name.

The channel - "pre-teen girl/sex pics" - is a dead giveaway. The chatters, dozens and dozens, are eager to share their perversions.

They want to swap tales and fantasies of the unspeakable kind. Better yet, they want to trade photos - sustenance for their sickness.

Immediately, the cyber sleuth gets a nibble. "Hey, how's it going?" asks one. Then another: "What age are you?"

Within seconds, he's inundated with inquiries. Some are seeking to break the ice; others get right to the point with raunchy talk.

It's just another day for state police Cpl. John Stepansky, an online investigator who spends much of his time trolling cyberspace in search of kiddie pornographers.

"My workload is constant," he concedes.

The 40-year-old Stepansky heads the computer crime unit for Troops D, headquartered at the Butler barracks.

His job is to investigate all crimes facilitated by computers; crimes such as identity theft, credit card fraud, electronic counterfeiting, telecommunications piracy and, of course, child pornography.

The latter crime takes up about 90 percent of his police work.

Stepansky's nearly life-long affinity for computers makes him a natural for the job.

"With this type of investigation you need to have kind of a knack for it," he said.

His boss, Sgt. James Martsolf, a crime section supervisor at the barracks, said the enjoyment of the high-tech gadgets is one reason that makes Stepansky a first-rate cyber crime investigator.

A strong work ethic is another.

"(Stepansky) loves what he does, obviously, and he spends a lot of time on his own getting the kind of training needed to do his job," Martsolf said.

Stepansky got hooked on computers during his junior year after enrolling in the first-ever computer class at McKeesport High School.

"Whatever I did there," he says, "it stayed with me."

The 19-year state police officer was the ideal choice as a computer crime investigator when headquarters saw a growing trend in computer crime.

Then a crime unit supervisor, he began plying his new trade in a part-time capacity in 1997, largely assisting the department's Bureau of Criminal Investigation track computer-driven criminals.

But the explosion in such crime necessitated the establishment of full-time computer crime units in all troops across Pennsylvania, including the one in Butler two years ago.

Stepansky was tabbed to work full-time for the unit that covers Butler, Armstrong, Beaver, Lawrence and Mercer counties.

He's essentially a one-man force in the computer crime unit, but knows he can rely on another specially trained officer at the Beaver barracks as well as a contingent of BCI computer crime investigators.

Other investigators at his home barracks also help out when he needs to get a search warrant as part of his investigations.

Stepansky's office is filled with tools of his trade: hardware and software galore. Notebook binders, bulging with online reference information, are everywhere.

He's surrounded by computers - a pair of desktops; a pair of laptops. A fifth is his state police network machine.

Back in the chat room, it's still noisy. Randomly, he clicks on a screen name. Below it is a tag line: "Tasty young flesh pics." Another name and another tag line: "Pre-teen pics 12 & younger."

"That's what they're advertising," Stepansky explained. "That's what they want. It's a trading deal where you can get in there and trade a picture with them; get some or send some."

He moves to another channel. This chat room is titled: "pre-teen boy sex pics." Again, no shortage of chatters, including one advertising "videos of boys getting spanked."

A message is sent to him: "What are you into?" Then more messages; some more disgusting than others. Stepansky barely bats an eye. He sees it everyday.

"I guess you become hardened by it - like investigating fatal crashes," he says. "You got a job to do and you do it."

Still, the father of three sons, ranging in age from 6 to 15, admits the images he encounters on the job are disturbing.

"You see some of these young children and they might remind you of someone you know," he says. "Those are the things that bring you back to reality. These are real people."

He points to the right side of the computer screen to show the screen names of all those in this chat room. He counts 73.

"And they're all talking to me," he says. "And that's just one channel. That's how prevalent the problem is."

All 73 on this channel are potential child pornography traffickers.

Stepansky and other computer crime investigators catch their share but they know they can't catch them all.

Child pornography cases are the bulk of Stepansky's investigations. He generates most of his own by targeting chat rooms frequented by those who dabble in kiddie porn.

He and other computer crime investigators disguise themselves in the online chats.

"We can be anyone we want in there, just like they can," Stepansky said. "We can make up the profile of a person as we go.

"People think they have anonymity on the Internet," he said, "and they do to some extent. But so do we."

Finding suspects can be as easy as shooting fish in a barrel. But his investigations are undertaken so as not to be subject to entrapment defenses.

"We're not looking to make criminals," he said. "We don't want to cause people to commit this crime."

He points out there is no doubt what's on the minds of those in chat rooms dubbed "young girls sex" and "pre-teen sex pics."

"We generally have them send us (pictures)," Stepansky said. "We do not send out pornography, child or otherwise. We let the person talk themselves into the crime - or I guess you could say, 'chat' or 'type' themselves into this crime."

Once kiddie porn is sent his way, Stepansky starts the process of identifying the bad guy. He primarily goes after those living in Pennsylvania and online over the World Wide Web.

"The obligation I see first of all is to the citizens of this commonwealth," he says. "So, I myself, particularly target commonwealth citizens that are into this type of thing."

His operating system allows him to click onto the chat room screen name to determine the Internet service provider (ISP) for that name.Next comes identifying the Internet protocol number. The IP number is unique for every computer connected to the Internet. The ISP assigns an IP address to each computer.Stepansky, when needed in his investigations, readily accesses the American Registry for Internet Numbers, which maintains a database of Internet protocol numbers.A search warrant is later prepared and served on the ISP to determine the identity of the person assigned to the IP number at the time the kiddie porn was transmitted.About three-quarters of Stepansky's child porn cases are self-generated. Other cases are referrals sent his way via the National Center for Missing and Exploited Children in Virginia, a kind of clearinghouse for child pornography complaints.The nonprofit center provides technical assistance to law-enforcement agencies in the investigation and prosecution of cases involving missing and exploited children.Internet service providers notify the center when they discover child pornography downloaded by their system's users. And the investigation is launched.The center, in turn, farms out the complaints to the federal Internet Crimes Against Children Task Force, which determines the agency, like the Pennsylvania State Police, that should handle the case and prosecution.Stepansky, who has handled more than a hundred such cases, serves the search warrant and helps seize computers, related equipment and any other evidence, including photographs, at the suspect's home.He said there is no standard personality profile for the kiddie porn suspects he's arrested. They have been as young as juveniles and as old as senior citizens."The one common factor is that every person I've ever arrested has been a male," he said.When he knocks on doors to serve the warrants, the reactions of suspects are similar."Typically, these people know they've done something wrong." Stepansky said. "Generally, we get great cooperation."He said most are embarrassed and most just want the officers to collect the evidence and leave as soon as possible."By the time they read the warrant they know that we've got them pretty much nailed," he said. "So it's not like they have very much to hide from."The evidence is taken back to the Stepansky's office and processed.Immediately, he disconnects the hard drive from the suspect's computer and copies it as an exact duplicate, which is used to review the contents for offending files.The forensic investigation entails examining images on the hard drive and identifying pornographic images that depict minors. The process is time-consuming but has been shortened with the use of a so-called "hashing" program.Stepansky explained each file, or image, has its own unique hash value - an alphanumeric value that identifies each image based on its content. The hash value is akin to a digital fingerprint.Using the program, he can identify the hash value of every incriminating file stored on a suspect's computer, and by running further searches, is able to cross reference hash values of identified images of child porn.The process reduces the time needed to study seized images, as Stepansky seeks to make his case.Once the offending images have been identified, they are copied onto a compact disc that goes into the investigative file to help prosecute offenders.Stepansky's cases have proven rock solid and air-tight. He's never had any of his evidence tossed by the court. And all but one arrest has ended in a plea. The lone exception was a guilty verdict rendered at trial."It's not gratifying to put somebody in jail," he said. "But we realize the gravity of what we're doing in these cases."It's not like we're trying to pick on 'Joe Citizen.' It's an illegal activity. There are victims. And you can see that by just looking at these kids - made to do horrible things."Beyond child porn cases, Stepansky investigates a plethora of computer-related offenses such as the burgeoning crime of identity theft.He also probes Internet auction site swindles, bomb threats and harassment via e-mail, check and currency counterfeiters, and general mischievous hacking, to name only a few.Stepansky is called upon to assist other criminal investigators in homicide, drug, arson and other cases. Colleagues often call on him for his technical expertise.He has received what he considers "premier training" in computer forensics from the state police as well as the National White Collar Crime Center in West Virginia.Additionally, he regularly attends classes and seminars in computer crime investigation offered at colleges or by the department or private companies.Some of his knowledge is self-taught. For instance, Stepansky on his own is learning a new computer operating system to supplement his proficiency in the Windows system."I like to tinker with his stuff," he explains. "I like to see how it works."He has also used his know-how to help train municipal police officers in a newly formed Computer Crime Task Force. The local officers use their computer-related training to aid in their own investigations and to assist other municipal departments.Created last year, the task force comprises officers from 31 local police departments - including Butler, and Butler, Cranberry and Middlesex townships - within state police Troop D, Butler; Troop C, Punxsutawney; and Troop E, Erie.Stepansky, meanwhile, feels fortunate to have parlayed his love of computers into a career of fighting crime: "It's a good gig for me."