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After 18-year-old David Ludwig allegedly shot and killed his girlfriend's parents and fled with her, Pennsylvania detectives collected evidence, dusted for fingerprints — and then went hunting for more clues in a surprisingly public, crowded place.

That place was cyberspace. Population: 1 billion and counting.

More specifically, police tapped into the Web logs — or online personal journals — of the double-murder suspect and his 14-year-old girlfriend, Kara Beth Borden. Each kept two blogs.

Although the Internet musings and chats haven't offered great insight into why Ludwig allegedly gunned down Borden's parents in their Lititz, Pa., home Nov. 13, they have helped investigators learn a little more about who he and Borden are.

They've also revealed the stress the young couple — both home-schooled in a small, religious Christian community — felt in a relationship that was secret at first and then forbidden by the girl's parents, largely because of the age difference and the fact that Borden is a minor.

Blogs are the latest form of electronic information that law enforcement is examining as part of investigations, and experts predict they'll become even more relevant as their popularity grows.

"We have to look at that as a new medium to solve crimes," said Cmdr. Christopher Vicino of the Pasadena, Calif., police department. "We would be able to use them, not so much as evidence, but more for investigative leads."

In one Sept. 17 online blog chat, a 17-year-old friend named Kayla tells Borden she's worried about her relationship with Ludwig and anxious because she's the only one who knows about it.

She tries to talk her friend out of her involvement, as a minor, with someone who is legally an adult.

"Brkndwnhnda (Kayla's screen name): Kara — at some point i need to have a serious discussion with you babe. sometime this week we have to get togther [sic] w/o butthead and talk. Just givin ya a heads up.

Karebear0005 (Borden's screen name): *raises eyebrow* ...

Karebear0005: if it has to do with david and me

Karebear0005: we are taking care of it

Karebear0005: we know what we are going to do

Brkndwnhnda: then dont expect me to keep this quiet. ...

Brkndwnhnda: i'm sick of the bsing around and the lies Kara ..."

Later in the chat, in a far cry from some of Borden's less hidden blog writings — many of which she signs "God Bless" — she tells Kayla not to get involved or try to help because "I have so much s*** on my mind."

Kayla eventually brings up the age difference and that sex with a minor is a crime.

"Brkndwnhnda: obviously you two dont care nuff that David may go to jail ...

Karebear0005: YOU DON'T UNDERSTAND WE TOOK THAT RISK THE FIRST NIGHT HE CAME OVER ...

Brkndwnhnda: you re 14 he's 18 and you're taking a huuuuuge risk! obviously you two dont care and neither to [sic] I!

Karebear0005: we dont care? about what

Brkndwnhnda: about the trouble you could cause if someone found out

Karebear0005: him might going to jail ...

Karebear0005: WE TOOK THAT RISK

Karebear0005:YOU CANT UNDERSTAND

Brkndwnhnda: ... i cant keep this a secret anymore! either you two are talking to me or i'm not keeping this quiet ...

Karebear0005: who are you gonna tell?

Karebear0005: hm

Karebear0005: his rents

Karebear0005: mine

Karebear0005: thanks a lot kayla"

It isn't yet clear whether Kayla was the one to tip off Borden's parents about the relationship, which court documents have described as "sexual," but the investigation is continuing.

Ludwig had some revealing posts on his blogs too, including a long string of pictures of himself. In some, the teenager made funny faces at the camera. In others, he held a sword and looked sinister.

The Ludwig-Borden case isn't the only recent one in which such Internet diaries have been a crime-solving thread. In September, the blog of a 17-year-old Virginia college student who disappeared and was later found dead, and that of a 38-year-old photographer who had had a romantic relationship with her, proved crucial.

Though the photographer, Ben Fawley, hasn't been formally charged with killing Taylor Marie Behl, he confessed to causing her death accidentally during "rough sex" and is in a Richmond jail on child pornography charges, still the focus of the investigation.

In another missing-person-turned-homicide case in Quebec, Kurt Lauder, 23, was arrested and charged with first-degree murder in the death of 16-year-old Shanna Poissant — whose body was found buried in the woods.

Police reportedly took Lauder into custody after the following anonymous tip was posted on the WhoKilledTheresa blog (dedicated to another unsolved-murder victim) and then sent on to them by the blogger:

"I was at a party near Hemmingford and was told that she was given extasy [sic] pills by Kurt Lauder and she overdosed. He then panicked and buried her body....Anonymus [sic]."

Lauder had already been a focus of the investigation, and detectives haven't commented on whether the Internet tip has factored into the case, but it could have at least corroborated what they already suspected.

"Blogs have actually assisted in some cases," said Helen Smith, a forensic psychologist in Knoxville, Tenn., who has a Web log available through her ViolentKids.com site. "There are crimes that have been solved or stopped because of blogs."

In the future, blogs could serve as tip lines for gumshoes and police departments.

"It's easier and more protected than a 1-800 tip hotline," said Robert McCrie, professor of security management at John J. College of Criminal Justice in New York. "The individual can put down what he or she wants to put down and isn't going to be interrogated by a trained person on the other line."

Both ill-fated couples, Borden and Ludwig and Behl and Fawley, chatted with each other on their blogs.

Behl's and Fawley's blogs on MySpace.com and LiveJournal.com have been taken down since her death and his arrest. Before that happened, some of their Web conversations were there for all to see.

One, which took place after the Virginia Commonwealth University freshman went to Fawley's off-campus apartment for the first time, was reprinted by The Washington Post on Oct. 3.

Behl had asked some of her 100 or so Web pals to post musings about her.

"This very attractive girl climbed up into my bunk @ 407, the last girl to do so before the move," wrote Fawley, screen name "Skulz67," in the first response to her request.

"well I was curious," Behl replied.

"...so was i ... fact I still am ..." agreed Fawley, who sometimes went by the screen name "Skulz."

Borden's and Ludwig's blogs on Xanga.com have been taken down since they were caught and he was arrested. Her MySpace blog is still set to private, and his MySpace page is still accessible.

Few direct online exchanges have turned up between Ludwig and Borden. Police now say Borden willingly went on the lam with Ludwig after he killed her parents, and prosecutors have dropped kidnapping charges against him.

In an Oct. 3 entry after "David" writes that he has just set up his MySpace blog, "Kara Beth" gushes:

"*YAY* heh you have to leave me a comment babe!! k? mk byeeeeeee lyl. <3Kara<3"

Her photo, taken while she was mugging for the camera, her eyes rolled upward, has been removed, as has her screen name — which now is listed as "nonya."

"People do bare their souls on blogs," Smith said. "A lot of these people are braggers."

Smith said it's especially common for boys to disclose information they might not tell others face-to-face, since they tend to be more tight-lipped than girls. Columbine shooters Eric Harris and Dylan Klebold, for instance, set up a Web site documenting their plot long before they carried it out. Unfortunately, no one paid much attention until after the fact.

"People do put their intentions up and [others] don't take them seriously, mostly because it's people they know and they don't think they're really going to do something," said Smith, who happens to be married to famed Instapundit.com blogger Glenn Reynolds.

There's another, even darker side to the blogs-and-crime phenomenon. Sometimes the modern-day journals open people up to being victimized by the many unsavory characters who troll the Internet. Online, predators can pretend to be whomever they want.

"Could stalkers pick up on blogs? Could criminals pick up on blogs?" wondered Keith F. Durkin, a criminologist at Ohio Northern University. "I could find out a lot about the car you drive, what your habits are. It concerns me from a security standpoint."

He and others say the key is to educate people — especially pre-teens and teens, among whom personal Web logs are heavily used — about the dangers, since those blogging and chatting from home online tend to have a false sense of security.

Those deciding to pen a "Dear Diary" in cyberspace should keep their sites private whenever possible so they have the right to accept or deny any "friend" who wants to link to them. They should also avoid posting too much personal information of any kind (last name, street address or hometown, photographs of cars with visible license plates, etc.) and be very careful about their correspondents.

"Any time you have communication on the Internet that's unfiltered and you don't really know who you're talking to, it could be a lure for criminals to exploit that situation," said Vicino, the Pasadena police commander. "You can pretend and lie. ... There's nothing to verify who you're talking to, and it's dicey."

Blogs do have their limits, of course — and their role in crime-solving is no exception.

Though cops don't need a search warrant to check Web logs remotely, it isn't so easy to use them as evidence in court.

Even pen-to-paper diaries aren't always admitted if their author can't definitively be proven, because hearsay is forbidden.

The standard of proof is even higher for online content because, unlike journals, blogs don't come with a person's handwriting to analyze or fingerprints to test.

"I have a hard time understanding how you can use a blog as evidence, short of hard corroboration of what is in it from some other source," said Jim Pasco, executive director of the Fraternal Order of Police.

"In and of itself, it's a handful of smoke."