ALFRED, Maine (NEWS CENTER) -- A psychologist testified Thursday that the 76-year-old Biddeford man accused of murder suffered a "mini-stroke" that caused behavioral change before the shooting.

James Pak has pleaded not guilty by reason of insanity to killing two teenagers in an apartment in December 2012. He's been charged with two counts of murder. Police were called to the building on Dec. 29, 2012 and determined that the landlord-tenant dispute over parking was civil. Moments later, police said that he shot Derrick Thompson, 19, Alivia Welch, 18, and Susan Johnson, 46. Johnson, Thompson's mother, survived and called 911.

In court Thursday, psychologist Kerry Drach said in the months leading up to the shooting, Pak's family noticed that his memory was poor and that he lost his temper more often.

Drach is the first witness in a hearing to determine if Pak is competent to stand trial.

Read more at the Portland Press Herald's website.