The oldest teen charged with murder in the death of 79-year-old Lila Warwick will soon have his mental health assessed.

A judge last week ordered a Dec. 19 mental examination of Brok Junkermeier, 19, who was indicted on first-degree murder charges for allegedly stabbing and strangling Warwick. Prosecutors say the plot was devised by Warwick’s grandson, Robert Warwick, whose next hearing is Dec. 20.

Kent Marshall, Junkermeier’s attorney, filed a notice in November saying that Junkermeier may rely on a defense that he is not guilty “by reason of mental illness or deficiency.”

Junkermeier appeared in court Monday, where Marshall argued that his client was not competent when he waived his Miranda rights before speaking to investigators. Marshall also claimed investigators did not have probable cause to search Junkermeier’s house. Judge Donald Spilseth has ordered both sides to submit arguments on those issues this month.

The youngest of the three defendants, 16-year-old Devon Jenkins, is to appear in court Tuesday. He faces second-degree murder charges for allegedly acting as lookout.