The Reston home where Scott Fricker and his wife Buckley Kuhn-Fricker were killed. (Cal Cary/For the Washington Post)

A teenager charged with killing his ex-girlfriend’s parents in December remains incompetent to stand trial, a judge ruled Wednesday in Fairfax County.

The now 18-year-old, of Lorton, was charged as a juvenile with the killings of Buckley Kuhn-Fricker, 43, and Scott Fricker, 48, on Dec. 22 in their Reston home.

The teen shot himself in the head after the attacks in which he was accused and was hospitalized with critical injuries before his eventual transfer to a juvenile detention center in Fairfax.

During Wednesday’s roughly three-hour hearing in Fairfax County Juvenile and Domestic Relations District Court, Judge Thomas P. Sotelo listened to testimony from five witnesses, including two clinical psychologists who have worked with the teen and three employees from the Fairfax County Juvenile Detention Center where he is being held.

The psychologists each suggested that brain damage the teen suffered after shooting himself have rendered him unable to fully understand trial proceedings and sufficiently assist his attorneys.

The Washington Post generally does not name juveniles charged with crimes unless they are charged as adults.

The teen’s mother has said previously that her son struggled socially and academically. He attended five schools in eight years, was often uncomfortable in social settings and had few friends. She said she was initially thrilled to find out her son had a girlfriend, until their relationship soured toward the end of last year.

The Frickers and other family members held an intervention for their daughter, imploring her not to see her boyfriend anymore due to his far-right views. In an email to the administrator of the teen’s school days before she was killed, Kuhn-Fricker called her daughter’s ex-boyfriend an “outspoken Neo Nazi.”

The teen’s mother said earlier this year that her son grappled with a bevy of mental health issues — school records indicated he was diagnosed with depression and autistic — but it wasn’t until after the December shootings that she became aware of his apparent ties to white supremacy.

William Ling, an expert in clinical neuropsychology, said at Wednesday’s hearing that his analysis of the teen in May suggests “significant impairment” and a “significant decline” from psychological tests he took in late 2017 — which can be attributed to damage to the left side of his brain.

He likened the teen’s cognitive ability during the May tests to someone who was “intellectually disabled,” and said the repetition of statements and questions, as well as the breaks required for the teen to understand trial proceedings, would “not be possible in normal court procedures.”

Ling said that with time, it would be possible for the teen to recover up to 80 percent of his previous mental capacity, but the progress typically takes 24 months.

The judge ordered the teen to return to court on Nov. 15 for a status update.

Justin Jouvenal contributed to this report.