In opening statements, First Assistant District Attorney Kevin R. Steele asked Common Pleas Court Judge Gary S. Silow to consider McAndrew's state of mind at the time of and just after the killings, and said evidence would show that "the defendant knew what he was doing" when he killed his family.
McAndrew also knew what he was doing after he put down the sword and dealt with investigators and psychological experts, the prosecutor said.
"We're dealing with a very intelligent person," Steele said.
McAndrew's lawyer, Paul A. Bauer III, said psychological diagnoses - including schizophrenia and bipolar disorder - and testimony from those who know McAndrew Jr. would justify a verdict of not guilty by reason of insanity.
"We're here trying to explain an irrational act in an irrational mind," Bauer said, explaining that his client had stopped taking his medications at the time of the killings.
Two Montgomery County detectives testified. One explained photographs of the bloody crime scene as they were projected onto a courtroom screen, and the other described a police interview with McAndrew.
During the interview, McAndrew wore black clothing stained with blood and gave police clear and correct answers to questions meant to gauge his awareness, Detective Christopher Kuklentz said. But when asked about the killings, McAndrew's answers turned incongruous, the detective said.
Police asked McAndrew what happened at the house and he replied, "It's a theory." When they asked if he had a sword, McAndrew said one word - "image," according to Kuklentz.
On cross-examination, Bauer pointed out that such "nonsensical" answers can be symptomatic of the type of schizophrenia that McAndrew has.
The defendant showed no emotion as sheriff's deputies escorted him into the courtroom, as he looked at the crime scene photos, or as a high school friend testified that the two of them and others were just "a bunch of good guys" who liked to hang out together.
The trial is scheduled to resume Monday and end Tuesday.