From the day a dead newborn baby was found in a Fayette County creek more than eight years ago, police operated on a theory: A local girl likely was her mother and a likely suspect.

They took that approach because where the infant was found -- in Cove Run Creek in North Union -- was a secluded area.

"If you don't live around here, you really don't know the road exists. It's a back road. It's not heavily traveled, not heavily populated," said state Trooper James A. Pierce, who investigated the case.

So police began gathering DNA samples from local women in the area with the hopes of tracking down the mother.

Eight years later, they got what they believe is the answer.

On Friday, the mother, Sarah Sue Hawk, a resident of North Union, was arrested and charged with homicide and concealing the death of a child. Ms. Hawk, now 25, is being held at the Fayette County Prison without bond.

Based on DNA evidence, police determined that Ms. Hawk is the mother of the infant, who was named "Baby Mary" by the county coroner.

Trooper Pierce said that over the years, police had gotten DNA samples from various young females living near where the baby was found in Cove Run Creek.

In January 2007, Mr. Pierce, who had been one of the initial officers at the scene but not the lead officer, got the case. About four or five females had already been tested, and Trooper Pierce tested "at least a half-dozen" more.

With the investigation, he said, "It was a lot of dead end roads. Over the past couple of years, I submitted a lot of DNA samples, and a lot of the girls have been cleared that live locally."

Ms. Hawk was among those initially interviewed after the newborn's body was discovered.

"She said at the time she wasn't pregnant. The investigators back then, they were pursuing other suspects," Trooper Pierce said.

Then last year, he started reviewing the list of girls who lived in the area.

"I discovered that she was never looked at," he said of Ms. Hawk.

The trooper contacted one of Ms. Hawk's four sisters, who voluntarily gave her DNA sample. State police then sent the sample to the New Jersey State Police Mitochondrial DNA Laboratory for analysis.

"It came back a hit," said Trooper Pierce, explaining that the results showed the baby was a relative of the woman.

"From there, I got search warrants (to gather DNA) for all five sisters, including Sarah."

The DNA swabs were sent to the Marshall University Forensic Science Center, where it was determined that Sarah Sue Hawk is the child's biological mother, police said.

Mr. Pierce said Ms. Hawk was 16 at the time the baby was born and had hid her pregnancy from her family and friends.

Investigators believe the baby was born alive. An autopsy showed the baby was at 8 1/2 months gestation and appeared to have been viable at the time of delivery, a police report stated.

The baby's body was found on June 4, 2000 by Scott Richard Hall and Allen Russell Hall, who had been trying to catch minnows for fishing. After Scott Hall noticed the same bag was in the creek a week earlier, they decided to open it.

"When they opened the bag, they discovered several more plastic bags that were all tied in knots and a backpack that was zipped up. After opening all the bags and unzipping the backpack, Allen Hall discovered a deceased infant inside the backpack wrapped in a flannel shirt," a police report stated.

State police, the county district attorney and the county coroner have scheduled a press conference Tuesday to discuss the case.