LINCOLN — Defense lawyers for Christopher Harris will hire an expert on violent video games as part of their effort to prove a theory that Harris killed a teenage boy in self-defense after the youth had bludgeoned to death four other family members in their Beason home.

Harris, 33, and his brother Jason Harris, 25, both of Armington, are charged with the 2009 killings of Rick and Ruth Gee and three of the couple’s children. Attempted murder charges against the pair relate to serious injuries suffered by a fourth child who has recovered.

In a motion filed Friday at a hearing in Logan County Circuit Court, defense lawyers Daniel Fultz and Peter Naylor asked that Dr. Craig A. Anderson, director of the Center for the Study of Violence at Iowa State University, be allowed to assist with their case.

Lawyers for Harris are expected to argue that their client walked in on a bloody melee in which 14-year-old Dillen Constant had killed his family and Harris was forced to kill the teen in self-defense. The defense has portrayed the boy as having mental health issues and a fondness for violent video games.

Illinois Assistant Attorney General Michael Atterberry did not object to hiring the expert.

McLean County Judge Scott Drazewski, appointed to replace Judge Thomas Harris, who is now hearing appellate court cases, also approved changes in filing deadlines leading up to the trial in Peoria County. A Feb. 15 date for the filing of all pretrial motions will be extended if needed before a March 1 hearing on the motions.

On April 19, the judge and lawyers will meet for what was described as “an open house” to familiarize themselves with the Peoria County court facilities. Drazewski moved the trial to Peoria in response to a defense motion.

The trial is scheduled to begin April 29 and is expected to last several weeks.

Jason Harris made a brief court appearance after his brother Friday, and a March 1 hearing was set to review the status of his case. No trial date has been set for Jason Harris, who is represented by Steve Skelton.

Two women who face obstruction of justice charges in the case have been subpoenaed for Chris Harris’ trial. Jennifer Earnest and her mother, Sara Duncan Sorrels, are accused of giving false alibis for Chris Harris.

Earnest is the former girlfriend of Jason Harris, and Chris Harris once was married to Rick Gee’s daughter, Nicole Gee, who was not among the homicide victims.

The brothers remain in custody.