The attorney for Green River killer Gary L. Ridgway says he is expected to plead guilty to a count of aggravated murder filed Monday in connection with the slaying of a 20-year-old woman who vanished after leaving a SeaTac motel in 1982.

"He takes responsibility for it," attorney Mark Prothero said Monday morning.

The woman, Becky Marrero, was long believed to be a victim of Ridgway, who confessed to her slaying when he agreed to plead guilty to 48 other murders eight years ago in a deal that likely spared his life. But it wasn't until December, after three teens stumbled upon her remains in an Auburn ravine, that prosecutors had the evidence they needed to charge Ridgway on Monday with her slaying.

In recent discussions with the serial killer, Prothero said he has indicated that he wants to plead guilty at his upcoming arraignment.

If Ridgway decides to plead not guilty, he could jeopardize the earlier plea deal and could potentially face the death penalty, according to the Prosecutor's Office.

Because Ridgway previously confessed to Marrero's killing, the new charge falls under the terms of his controversial 2003 plea agreement, prosecutors said.

If Ridgway enters a guilty plea to Marrero's death, he will maintain his current status of serving life in prison without the possibility of parole under the agreement, according to the Prosecutor's Office. During a news conference Monday morning, King County Prosecutor Dan Satterberg said he expects Ridgway will plead guilty.

When Ridgway is arraigned on Feb. 18 at the Norm Maleng Regional Justice Center in Kent, it will be the first time he has set foot in a King County courtroom since he was sentenced on Nov. 5, 2003, prosecutors said.

In 2003, Ridgway told investigators the general location where he believed he disposed of Marrero's remains, but members of King County's Green River Task Force could not find her remains.

Marrero's remains were found in December in a ravine in the 6300 block of 296th Street, just west of West Valley Highway North, an area near where Ridgway disposed of the remains of murder victim Marie Malvar. Ridgway previously pleaded guilty to Malvar's killing.

The remains of three other Ridgway victims have been found but never identified. Ridgway implied that the three were killed in spring or summer 1983.

According to the Sheriff's Office, the remains belonged to:

• A white female, possibly as young as 12; found March 21, 1984, in the Burien area off Des Moines Memorial Drive South.

• An African-American or possibly mixed-race female; found Dec. 30, 1985, near Mountain View Cemetery in Auburn. She was likely between 18 and 24 when she died.

• A white female, between 14 and 18; found Jan. 2, 1986, near Mountain View Cemetery in Auburn.

Also in 2003, Ridgway claimed to have killed three other women: Kelly Kay McGinness, 18; Kassee Lee, 16; and Patricia Osborn, 19. But the women's remains have never been found, and he wasn't charged in their slayings because of a lack of sufficient evidence.

Jennifer Sullivan-Seattle Times