NEW YORK >> The four bodies were discarded and hidden in the deep brush along Ocean Parkway on Long Island over a three-year period. They were all women, thought to be killed by the same person.

And once the victims were identified in January, another common thread emerged: They were all prostitutes who advertised their services on Craigslist.

As websites like Craigslist and Facebook have grown in popularity, they have become a resource both for criminals to solicit potential victims and for law enforcement officials in search of suspects.

Terror suspects have plugged into the idea of cybersurveillance to view live traffic feeds just as robbers might case look over a bank from the comfort of home. Law enforcement has followed the criminals to these online outposts, just as they would follow an informant’s nod to some back alley where a suspect was hiding.

“In my time, in the last decade, it has become increasingly of greater assistance to law enforcement,” John F. Timoney, who served as first deputy commissioner in New York and as chief of the Miami police, said of the Internet. “In the old days, the flim-flam might have been in front of a bank, or grocery store, where you met the person, where the beginnings of the crime took place. And now it’s on Craigslist.”

The authorities on Long Island are hoping that Craigslist, as well as other online sites, will help lead to answers in the Ocean Parkway homicides. So far, 10 sets of human remains have been found in the dunes north of the parkway along the Atlantic Ocean; only the first four have been identified.

An early step has been discerning what clues might be found in all the cyberspace detritus of the four women’s lives.

Each of them — Megan Waterman, 22; Melissa Barthelemy, 24; Maureen Brainard-Barnes, 25; and Amber Lynn Costello, 27 — left behind a digital data trail that detectives can mine for photographs, phone numbers and more. Craigslist stores classified postings and the Internet Protocol addresses of the computer used to post them. The site might also have email addresses for clients who replied to an advertisement.

From there, detectives with a court order, subpoena or a declaration of an emergency could contact the Internet service providers of the women, and of their clients, to look through emails for correspondence. A cellphone number from an email or a Web log archived by Craigslist could lead down another path: Investigators could contact the cellphone company to obtain call records, stored text messages and geographic location data that reveal approximately where people have been and when.

The Internet Protocol address — unique numbers identifying a computer’s network connection on the Web — can lead to a computer’s physical location, once a cable or phone company divulges where the subscriber was hooked up.

All the data and electronic leads are being carefully analyzed and evaluated, Dominick Varrone, the chief of detectives at the Suffolk County Police Department, said in an interview.

“Obviously, that is the ongoing emphasis and focus of this investigation,” he said, declining to detail the progress investigators have made on this front.

“We were able to quickly identify those women,” Varrone said. “We have an assigned homicide task force that has been looking at everything; computer records, telephones, and any way you can compare. All of that has been analyzed and has been looked at.”

When investigators in Boston were looking for a suspect who killed a woman and attacked another, both of whom had advertised massage services on Craigslist, the electronic trail of evidence and clues was substantial.

Through computer and phone records, detectives were able to establish a direct link to the eventual suspect, Philip Markoff, a 22-year-old medical student. In need of an image of the suspect, they did not have to look far: His photo was on his Facebook page.

“Once we got those communications and we were able to track the IP address with subpoenas, it was fairly easy to track a suspect in that case,” said Edward Davis, the police commissioner in Boston. “We expected it to be much more complicated.”

Markoff, who became known as the Craigslist killer, killed himself while in custody, a little more than a year after his arrest.

In 2009, Craigslist closed down its “erotic services” section — a thinly veiled forum for offering sex services — partly because of pressure from a number of state attorneys general, though similar ads have since appeared at times in other parts of the website.

Craigslist may disclose information about its users if the law requires. It may give data to law enforcement “in the good faith belief that such disclosure is reasonably necessary,” according to its privacy policy. Susan McTavish, of Craigslist, would not say how many annual requests for information that Craigslist gets from law enforcement.

Timoney said society has yet to think through all the thorny legal issues, like questions on invasion of privacy connected to law enforcement’s surveillance of Internet advertising and social networking sites. “The courts haven’t really chimed in yet,” he said. “But they are going to. It is only a matter of time before one of these cases goes to the Supreme Court.”

Some analysts believe the move by Craigslist to ban adult services may actually impede law enforcement because that activity has been pushed from an observable platform to sites less easily monitored or controlled. Other websites exist as a marketplace for arranging meetings for sex, and at least two of the victims found on Long Island used those as well.

In Waterman’s case, her online presence is still alive in an advertisement on the adult services website, www.myproviderguide.com.

“hi, my name is lexy,” it says. “I have blond hair blue eyes great attitude I love what I do ur time with me is never rushed please no blocked calls and text messages thanks hope 2 hear from u soon.”

It ends by providing a phone number with a Maine area code.

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