TULSA, Okla. — An attorney for an Oklahoma teenager charged with his older brother in the stabbing deaths of their parents and three siblings may try to use an insanity defense at the trial.

Michael Bever, 17, has pleaded not guilty to five counts for first-degree murder and one count of assault and battery with intent to kill in the July 2015 attack at their family home in a Tulsa suburb. Authorities say Bever and his brother, 20-year-old Robert Bever, killed their parents and three of their siblings, ages 5, 7 and 12. Two other siblings survived.

Robert Bever pleaded guilty in the case and was sentenced to life in prison without the possibility of parole.

Michael Bever’s attorney, Rob Nigh, notified the court Thursday that he intends to raise the question of his client’s mental status at the time of the killings, the Tulsa World reported (http://bit.ly/2dxWXA9 ). The court filing doesn’t mean Nigh will definitely pursue the mental health defense, but it leaves him the option to do so if “it is appropriate.” Nigh indicated during the Sept. 7 arraignment that he would use such a defense.

Nigh said Bever’s mental status at the time of the attacks is still under evaluation, however if the evaluation finds that a mental health defense isn’t appropriate, attorneys will withdraw the notice.

A discovery hearing is set for April 11, with a jury trial set for June 5.

Michael Bever remains jailed without bond.

Information from: Tulsa World, http://www.tulsaworld.com