What could prompt two 15-year-old girls to kill anyone, much less an adoptive mother?

Defense attorneys and prosecutors will wrangle with that question in coming weeks during the trial for Brenda and Catherine O’Connell in Gwinnett County. Jury selection began this week.

Authorities say the teenage girls, adopted at separate times from Guatemala, strangled 57-year-old Muriel O’Connell during a Aug. 6, 2006 dispute at their home in Buford.

Brenda and Catherine were 15 when the alleged slaying occurred. They are now 17 years old. They will be tried together as adults, each facing murder charges that could put them behind bars for life.

Lawyers representing the girls say it will be a complicated case.

“We have international adoption with single mother, we have self defense, we have psychiatric issues, just pretty much everything you can think of to put in a trial is in this trial,” said defense attorney Hillary Krepistman.

Krepistman represents Catherine, who was adopted by O’Connell at age 11 from a group home in Guatemala. Three years later, O’Connell adopted Brenda at age 14 from the same group home. The girls are not related by blood.

The sisters reportedly told a neighbor that their mother tried to stab them and they killed her in self-defense. They also claimed they had been abused by their mother in the past.

Authorities have offered no motive for the slaying to date.

Several weeks prior to O’Connell’s death, the Department of Family and Children Services began looking into problems with the family. Prosecutors said there had been an allegation that the girls once tried to poison her.

O’Connell apparently said she feared for her life only a few hours before being killed, neighbors told the Journal-Constitution in an earlier report.

Mental health experts have been retained by both sides to examine the girls and testify at trial.

Deputy Chief Assistant District Attorney Dan Mayfield said he plans to introduce “lots of different types of evidence, from psychological evidence to DNA to crime scene analysis.”

Opening statements are expected to begin some time next week.