A Dead Baby Was Found at an Airport in 2005. Her Mother Was Just Arrested.

The dead baby girl was found in a trash bin in a women’s bathroom at main airport in Phoenix on Oct. 10, 2005. Wrapped in newspapers and a towel, the newborn had been stuffed into a plastic bag from a Marriott Hotel, the police said.

Detectives immediately began investigating the death of the child, who came to be known as Baby Skylar. A medical examiner determined two days after the baby was found that she had been suffocated and was the victim of a homicide. But leads in the case eventually dried up, and the investigation remained dormant for years.

On Tuesday, more than 18 years after the gruesome discovery at Terminal 4 of Phoenix Sky Harbor International Airport, the authorities announced at a news conference that they had identified and arrested the baby’s mother, Annie Anderson, 51, of Washington State, and that she would be charged with first-degree murder in the child’s death.

Ms. Anderson was in custody in Washington on Tuesday, and was awaiting extradition to Maricopa County, Ariz., Lt. James Hester of the Phoenix Police Department said at the news conference.

Among the few and early leads that the police had was the plastic bag in which the baby’s body had been found. That prompted detectives to investigate Marriott hotels in the Phoenix area, Lieutenant Hester said. But those leads and others proved unsuccessful.

Then, in 2019, the Phoenix police partnered with the F.B.I. to use genetic genealogy, an emerging tool in solving cold cases, to look into the Baby Skylar mystery, Lieutenant Hester said.

Dan Horan, a supervisory special agent with the F.B.I. field office in Phoenix, said at the news conference that the two agencies used a process known as investigative genetic genealogy, which uses existing D.N.A. evidence from an unknown person and tries to find family members based on publicly available genealogy databases.

In doing that, the two agencies were able to find a possible relative of Baby Skylar. That relative, whom the authorities did not identify, agreed to share a sample of their D.N.A. with the authorities for one-time use, Agent Horan said.

In January 2022, investigators traveled to Washington State, where they executed a search warrant and interviewed Ms. Anderson, the authorities said. Lieutenant Hester said that Ms. Anderson confirmed that she was the mother of Baby Skylar and gave the police an account of what had happened.

“We have a dead child, we have an identified mother, and we have her statement,” Lieutenant Hester said.

The authorities declined to share details of Ms. Anderson’s account. From the investigation, the authorities learned that Ms. Anderson was visiting Phoenix in October 2005 on business for a real estate boot camp, and that the child, most likely, was not born at the airport, Lieutenant Hester.

It was not immediately clear on Tuesday whether Ms. Anderson had a lawyer.

During the investigation, the authorities were also able to identify the baby’s father, and he was found to have no “criminal culpability,” Lieutenant Hester said. The authorities did not name the father.

Sgt. Rob Scherer of the Phoenix Police Department said on Tuesday that the investigation “touched many people at many different levels of this department and beyond” and that it “will stick with a lot of officers that have been involved.”