Kao Chongsua Xiong’s shoulders heaved and he sobbed uncontrollably, his wails drowning out a medical examiner’s testimony of how a single bullet fired by his 4-year-old son tore through the aorta of his youngest child, killing the toddler.

Still, he refused to look away from the images of 2-year-old Neegnco Xiong’s lifeless body, shown to a jury in the final day of testimony Wednesday in Xiong’s trial on charges he contributed to his son’s death by improperly storing the gun that killed him.

“He was a perfectly healthy boy,” deputy Hennepin County medical examiner Dr. Enid Boeding testified, describing Neegnco’s condition before he was shot on Dec. 5, 2012, by his older brother, who was playing with a loaded handgun in an upstairs bedroom while their parents were downstairs making lunch.

The shooting led to felony manslaughter and child endangerment charges against Xiong, 31, who prosecutors allege was negligent for stashing the weapon next to a mattress between a pillow and headboard where the children played unattended. The gun was one of eight police found in Xiong’s south Minneapolis home. A third count of gross misdemeanor child endangerment alleges that, other than a few plastic horses and a toy gun, there were no other toys anywhere in the house, where the children slept on the floor in the second bedroom.

During cross-examination by Xiong’s lawyer, Steve Meshbesher, Hennepin County medical examiner death investigator Carrie Notch testified that she arrived at the scene to find Xiong with his hands and clothes covered in his son’s blood. His wife was curled in a ball in the living room while their older son sat on the couch. She said Xiong “had pretty much a blank stare on his face,” and cried when she told him that Neegnco was dead.

“Was it sad?” Meshbesher asked.

“Yeah,”she said. “It was very sad.”

Boeding explained to the jury that the bullet struck the toddler’s right shoulder, traveled downward through his chest and exited through the left side of his body. Xiong wept as she pointed out the holes in the boy’s red T-shirt, and the abrasions caused by the close-range gunshot.

She said that although some medical examiners may have classified the case a homicide, Hennepin County ruled that it was an accidental death.

She told assistant Hennepin County attorney Amy Sweasy that a boy the age of Neegnco’s brother does not understand how dangerous firearms are.

“A 4-year-old does not possess the capacity to understand how dangerous it is to point a loaded firearm at someone and pull the trigger,” she said. “Further, a 4-year-old does not understand the concept of death.”

Following Boeding’s testimony, Xiong continued to wail during a short break, while family members tried in vain to console him. He regained his composure to return the courtroom to waive his right to testify.

“Do you think you are in a good position to decide whether you want to testify or not?” Judge Daniel Moreno asked the visibly-shaken Xiong.

“Yes, your honor,” Xiong said.

The case is expected to go to the jury Thursday afternoon after closing arguments.