Laird in her closing placed blame on Lucky Gunner, a Tennessee-based online retailer which sold the shooter more than 100 rounds of ammunition without verifying he was old enough to buy it. Lucky Gunner was a defendant in the lawsuit until last year, when it reached a settlement with the families.

She also said the school was at fault for lapses including not notifying the shooter’s parents about his absences from school and about his habit of wearing a trench coat — what the plaintiffs’ lawyer characterized as a red flag signaling his admiration of school killers like the shooters at Columbine High School in Colorado.

She disputed McGuire’s account of the location of the keys to the gun cabinet, saying the keys were on top of a cabinet in the parents’ bedroom, not in a shared space. “They did more than their duty required of them, and they did it willingly to try to safely store their guns,” she said.

The shooter worked to hide his violent plans from his family and presented almost no signs of the crisis brewing underneath the surface, she argued.

“If he had been breaking the law, if he had been violent, if he had been using drugs, if he had been abusing animals or setting fires or holding a magnifying glass on ants, anything, then maybe you’d go hmm, we need to look at that,” she said. “He had slipping grades, but he never failed. He started to want to spend a little bit more time alone. These were the two main things that you saw.”

“There was no indication of any depression or deep, serious mental illness, or any mental illness at all,” she said.

CNN’s Amy Simonson and The Associated Press contributed to this report.