A woman and her boyfriend were charged Friday with aggravated first-degree murder in the methodical Christmas Eve shootings of her parents, her brother, his wife and their two young children.

Michele K. Anderson and Joseph Thomas McEnroe, both 29, confessed to detectives they had shot six members of Anderson's family, according to court documents. Anderson said both of them shot her parents, brother and sister-in-law, while McEnroe killed the children, according to a separate affidavit.

King County Prosecutor Dan Satterberg, who will decide whether to seek the death penalty, said the motive for the slayings may never be known.

"Given the magnitude of this crime, I pledge to give this case serious consideration for the state's ultimate penalty," Satterberg said.

Anderson and McEnroe were each charged with six counts of aggravated first-degree murder. The aggravated circumstances underlying the charges include that there were multiple victims, and that two killings — the shootings of the children — were done to conceal a crime or the perpetrators' identity.

Conviction on aggravated first-degree murder in Washington is punishable only by death or life in prison without possibility of parole.

Anderson and McEnroe were ordered held without bail after an initial court hearing Thursday.

In police affidavits filed in court Thursday, King County Sheriff's Detective John Pavlovich described the horrific killings he said McEnroe outlined to authorities, but the detective made no mention of motive.

First, Pavlovich wrote, McEnroe and Anderson shot her parents, Wayne Anderson, 60, and Judy Anderson, 61, with large-caliber pistols and dragged the bodies to a shed. A short time later, the Andersons' son, Scott, his wife, Erica — both 32 — and their children, Olivia, 6, and Nathan, 3, arrived for a Christmas Eve visit.

"Knowing that Scott and his family were potential witnesses, Joe and Michele shot them," Pavlovich wrote. His affidavit said McEnroe shot all four.

McEnroe and Anderson confessed to authorities, court documents said. Anderson said both of them shot her parents, brother and sister-in-law, and McEnroe killed the children, according to a separate affidavit. It also does not give a motive.

McEnroe and Anderson, who had been together for six years, lived in a trailer about 200 yards from her parents' house. After the killings, they tried to flee to Canada, court documents said, but they returned the following day and were detained.

At Thursday's hearing, both defendants waived their right to appear before a judge.

McEnroe appeared briefly in the courtroom, then left with his attorney. The attorney, Devon Gibbs, did not return a call for comment Thursday.

Anderson's attorney, public defender George Eppler, said Thursday he spoke with her briefly before the hearing. "We limited our conversation solely to the issue of today's court appearance," Eppler said.

The bodies were found Wednesday morning on Wayne and Judy Anderson's property near Carnation, about 25 miles east of Seattle, by one of her co-workers, who was worried when Judy Anderson did not show up for work.

Ben Anderson, the elder couple's grandson, has said money could have been a factor in the deaths. "She felt she wasn't loved enough and everyone didn't appreciate her and she was pushed out of everyone's life," he said Wednesday night, referring to Michele Anderson.

McEnroe's mother, Sean Johnson of Minneapolis, said she hasn't had much contact with McEnroe since he cut ties with his family after a dispute over money.

She told The Seattle Times that her eldest son was a "good Christian" and she was shocked he had been arrested in the slayings.