Jury selection continued Thursday in the trial of a 15-year-old accused of the suffocation killings of his teenage sister and her friend.

Attorneys for Daniel Betournay concede their client committed the slayings, but plan a defense that he was not criminally responsible for his actions.

His lawyers maintain Betournay suffered from diminished capacity and couldn’t mentally form an intent to kill the girls or premeditate the acts.

The jury will be asked to decide among four degrees of homicide, or acquittal, he said.

The prosecution must prove that Betournay had the necessary mind-set that would make the killings criminal under Washington state law.