As the fourth anniversary of the slayings of her daughter, son-in-law and grandchildren inches closer, Pam Mantle is facing the prospect that it could be another year before the two charged with the killings face a jury.

Michele Anderson, 33, and her ex-boyfriend, 32-year-old Joseph McEnroe, face capital murder charges after police discovered a massacre inside the home of Anderson's parents on Dec. 24, 2007.

In all, six people were killed — Anderson's parents, Wayne and Judy Anderson; her brother, Scott Anderson; her sister-in-law, Erica Anderson, and the couple's children, Olivia, 5 and Nathan, 3.

Mantle and her family have attended nearly every court hearing, as Anderson has fired and fought with her lawyers, and confessed her guilt in open court. Mantle has patiently watched and waited as attorneys have come and go and delays have pushed the trial date back, and then back again.

She hasn't complained much, Mantle said. Until now.

On Friday, Supreme Court Commission Steven Goff published a ruling that could delay the case for a year while Anderson and McEnroe's lawyers argue over which of them should go to trial first.

Initially, prosecutors had sought to try the pair together. The case was split into two trials earlier this year. Jury selection was set to begin within the next few months, with a trial beginning early next year.

The King County Prosecutor's Office said it will ask the commissioner to reconsider, and appeal if he doesn't, said office spokesman Dan Donohoe.

"The crux of the issue is who is going to be tried first. This is a discrete, finite issue that well could delay the case for up to a year," said Senior Deputy Prosecutor Scott O'Toole, who is handling the case. "There is a total lack of a sense of urgency."

The Supreme Court is being asked to decide how the trial judge should determine who will be tried first, O'Toole said.

McEnroe had appealed to the state Supreme Court after prosecutors had said they intended to try his case first. Anderson joined the appeal later. Briefs in the appeal have been filed under seal because the attorneys say the documents contain mental-health information they don't want given to the prosecution or publicized in the media.

In his ruling, Goff said the court will hear additional arguments on the issue Feb. 14. It could be months before the justices rule.

A new trial date will likely be discussed at Anderson and McEnroe's next King County court hearing on Sept. 21.

"I'm just so sick of waiting. I just think the whole thing is ridiculous," Mantle said. "It's just adding another layer onto the damned misery cake. This is just a slap in the face."

Seattle Times news researcher Miyoko Wolf contributed to this report.

Jennifer Sullivan: 206-464-8294 or jensullivan@seattletimes.com