Brennan Nowell was able to hold on for nearly five hours after a bullet pierced his 31-pound body just before Christmas, according to a Hamilton County Medical Examiner's Office autopsy report released Wednesday.
The bullet flew at an angle through the front of the 2-year-old's chest, entering just below his right breast and exiting from his upper left breast, the report states.
Brennan was taken to T.C. Thompson Children's Hospital at Erlanger, where he later died. The probable cause of death was the gunshot wound, according to the report.
The report also releases new details of how the shooting happened at the Harrison home of Brennan's grandparents, Stan and Janet Nowell.
On the night of Dec. 20, Brennan's grandfather left a .40-caliber semi-automatic pistol on a chair in the family's house on River Stream Drive, according to the report. Brennan grabbed the gun and accidentally shot himself.
"He was a beautiful boy that leaves behind countless people who loved him and nurtured him," his obituary reads. "We will always be blessed for what time we had with him and will pray for the day that we get to see him again."
The investigation continues, but the Hamilton County Sheriff's Office has not released any additional information about the shooting, spokeswoman Janice Atkinson said.
Brennan is one of three Chattanooga-area children under the age of 14 to die of accidental gunshot wounds in 2012.