In the end, it wasn't a fingerprint or a blood spatter that led authorities to the woman suspected of strangling a mother-to-be and cutting the baby from her womb.

It was an 11-digit computer code.

Police zeroed in on Lisa Montgomery (search) in the most 21st century of ways, by trolling computer records, examining online message boards and — most important — tracing an IP address, 65.150.168.223, to a computer at her Melvern, Kan., home.

"That in and of itself led us to the home," Jeff Lanza, an FBI spokesman here said of the IP, or Internet protocol, address, the unique number given to every Internet-connected computer.

Investigators say that just before the slaying, Montgomery had corresponded over the Internet with the victim, Bobbie Jo Stinnett (search), about buying a dog from Stinnett. The same technology that makes instantaneous communication possible enabled authorities to crack the case in a matter of hours and rescue the premature baby.

Montgomery, 36, awaited her first court appearance Monday at the federal courthouse in Kansas City. She is charged with kidnapping resulting in death. Authorities said she confessed to the crime. The 4-day-old girl was reported in "remarkably good" condition Monday.

Within hours of Stinnett's killing Thursday at her Skidmore, Mo., home, investigators realized the potential information her computer could hold in finding her killer.

Stinnett, 23, raised rat terrier dogs at home and had been expecting a potential customer the afternoon she was killed. In fact, she had to get off the phone with her mother because the customer was at the door, according to investigators.

When Stinnett's body was discovered, detectives collected not just physical evidence; they also took her computer.

In addition to trying to find the killer, investigators were racing against time to find the baby, who was one month premature when she was cut from her mother's belly and, it was feared, may have suffered oxygen loss or other trauma when her mother was strangled.

At the lab, clues seemed to pour out of the computer within minutes — who Stinnett had been e-mailing, what sites she had been visiting. Important tips from the public came in, too. Among them: a North Carolina dog breeder pointed to communications on a rat terrier message board.

"My adrenaline just started rushing," said the breeder, Dyanne Siktar. "I knew they could track the IP."

It turned out that at 4:22 p.m. on Wednesday, the day before Stinnett's slaying, someone identifying herself as Darlene Fischer posted a message to the victim on a rat terrier message board. "Please get in touch with me soon as we are considering the purchase of one of your puppies," it said.

About an hour later, Stinnett communicated with Fischer for about 20 minutes, investigators said. Then, at 7:44 p.m., Stinnett posted a message to Fischer: "I've e-mailed you with the directions so we can meet. I do so hope that the e-mail reaches you. Great chatting with you on messenger. And do look forward to chatting with you tomorrow a.m."

Investigators traced Fischer's IP address back to a dial-up connection from the Melvern home of Montgomery and her husband. He has not been charged with any wrongdoing.

On Friday, less than 24 hours after the slaying, investigators pulled up to the couple's home in Kansas, found the baby and arrested Montgomery.

As for how the killer knew Stinnett was about to become a mother, Stinnett had a Web site about her dogs that investigators said may have included a picture of Stinnett pregnant. The FBI would not comment on whether the pair had ever met before last week, or how the killer knew Stinnett was still pregnant.

Authorities most often use computers to catch sexual predators, hackers and other white-collar criminals. But they are increasingly being used to solve violent crimes, too.

Experts say IP addresses are not foolproof; they can be made up, like nearly anything else in the Internet age. But they often are part of a package of evidence that can lead to a conviction.

"Quite often, in the past, detectives would walk past the computers at the crime scene and look at the hairs and fibers and fingerprints," said FBI agent Tom Maiorana, director of the bureau's Regional Computer Forensic Laboratory here. "Now we're seizing the computers and finding out a tremendous amount of information about the lives of the people involved."